It is currently 19 Nov 2017, 23:32

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# What is the greatest possible area of a triangular region

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Manager
Joined: 18 Oct 2009
Posts: 50

Kudos [?]: 768 [3], given: 3

Schools: Kellogg
What is the greatest possible area of a triangular region [#permalink]

### Show Tags

01 Nov 2009, 22:12
3
KUDOS
12
This post was
BOOKMARKED
00:00

Difficulty:

65% (hard)

Question Stats:

54% (00:55) correct 46% (01:02) wrong based on 630 sessions

### HideShow timer Statistics

What is the greatest possible area of a triangular region with one vertex at the center of a circle of radius one and the other two vertices on the circle?

A. $$\frac{\sqrt{3}}{4}$$

B. $$\frac{1}{2}$$

C. $$\frac{\pi}{4}$$

D. 1

E. $$\sqrt{2}$$
[Reveal] Spoiler: OA

_________________

GMAT Strategies: http://gmatclub.com/forum/slingfox-s-gmat-strategies-condensed-96483.html

Last edited by Bunuel on 17 Oct 2013, 08:49, edited 1 time in total.

Kudos [?]: 768 [3], given: 3

Senior Manager
Joined: 18 Aug 2009
Posts: 299

Kudos [?]: 362 [0], given: 9

Re: Maximum Area of Inscribed Triangle [#permalink]

### Show Tags

02 Nov 2009, 02:36
1
This post was
BOOKMARKED
gmattokyo wrote:
I'd go with B. 1/2
right triangle. a rough sketch shows that taking one of the sides either left or right seems to be reducing the area.

right triangle area =1/2x1x1 (base=height=radius)=1/2

The logic just striked me... area=1/2xbasexheight.
In this case, if you keep the base is constant=radius. Height is at its maximum when it is right triangle.

is that the OA?

Kudos [?]: 362 [0], given: 9

Director
Joined: 25 Oct 2008
Posts: 594

Kudos [?]: 1182 [0], given: 100

Location: Kolkata,India
Re: Maximum Area of Inscribed Triangle [#permalink]

### Show Tags

03 Nov 2009, 17:58
So I came across this question in my test and got it wrong..I assumed the equilateral triangle has the greatest area and marked root3/4
Now i see the logic..any triangle drawn by the above specifications will have two legs as the radius..we have to maximise the area so the third leg should be the largest.

However,is this some kind of a theoram/fact that we should be knowing?That to get the largest area of a triangle,the triangle has to be a right angle and not an equilateral one?
_________________

http://gmatclub.com/forum/countdown-beginshas-ended-85483-40.html#p649902

Kudos [?]: 1182 [0], given: 100

VP
Joined: 05 Mar 2008
Posts: 1467

Kudos [?]: 307 [0], given: 31

Re: Maximum Area of Inscribed Triangle [#permalink]

### Show Tags

03 Nov 2009, 18:53
tejal777 wrote:
So I came across this question in my test and got it wrong..I assumed the equilateral triangle has the greatest area and marked root3/4
Now i see the logic..any triangle drawn by the above specifications will have two legs as the radius..we have to maximise the area so the third leg should be the largest.

However,is this some kind of a theoram/fact that we should be knowing?That to get the largest area of a triangle,the triangle has to be a right angle and not an equilateral one?

Yes, if the bases are the same. In this case 1 would be the base (radius) and a 45-45-90 maximizes area

Try using any number for the base, for example 4

45-45-90 = 1/2(4)(4) = 8

60-60-60 = 1/2(4)(2 sqrt(3)) = 4 sqrt(3)

Kudos [?]: 307 [0], given: 31

Math Expert
Joined: 02 Sep 2009
Posts: 42256

Kudos [?]: 132742 [6], given: 12360

What is the greatest possible area of a triangular region [#permalink]

### Show Tags

06 Dec 2009, 12:47
6
KUDOS
Expert's post
8
This post was
BOOKMARKED
What is the greatest possible area of a triangular region with one vertex at the center of a circle of radius one and the other two vertices on the circle?

A. $$\frac{\sqrt{3}}{4}$$

B. $$\frac{1}{2}$$

C. $$\frac{\pi}{4}$$

D. 1

E. $$\sqrt{2}$$

Clearly two sides of the triangle will be equal to the radius of 1.

Now, fix one of the sides horizontally and consider it to be the base of the triangle.

$$area=\frac{1}{2}*base*height=\frac{1}{2}*1*height=\frac{height}{2}$$.

So, to maximize the area we need to maximize the height. If you visualize it, you'll see that the height will be maximized when it's also equals to the radius thus coincides with the second side (just rotate the other side to see). which means to maximize the area we should have the right triangle with right angle at the center.

$$area=\frac{1}{2}*1*1=\frac{1}{2}$$.

You can also refer to other solutions:
triangular-region-65317.html
_________________

Kudos [?]: 132742 [6], given: 12360

Manager
Joined: 29 Oct 2009
Posts: 209

Kudos [?]: 1658 [15], given: 18

GMAT 1: 750 Q50 V42
Re: GMAT Prep Triangle/Circle [#permalink]

### Show Tags

06 Dec 2009, 13:09
15
KUDOS
3
This post was
BOOKMARKED
Adding onto what Bunuel said, there is an important property about isosceles triangles that will help you understand and solve this question.

First though, let us see how this particular triangle must be isosceles.

If one vertex is at the centre of the circle and the other two are on the diameter, then the triangle must be isosceles since two of its sides will be = radius of circle = 1.

Now for an isosceles triangle, the area will be maximum when it is a right angled triangle. One way of proving this is through differentiation. However, since that is well out of GMAT scope, I will provide you with an easier approach.

An isosceles triangle can be considered as one half of a rhombus with side lengths 'b'. Now a rhombus of greatest area is a square, half of which is a right angled isosceles triangle. Thus for an isosceles triangle, the area will be greatest when it is a right angled triangle.

[Note to Bunuel : I think this one might have been missed in the post on triangles?]

Now for the right angled triangle in our case, b = 1 and h = 1

Thus area of triangle = $$\frac{1}{2}*b*h$$ = $$\frac{1}{2}$$

Note : I believe the mistake you might have made is considered the base to be = 2 (or the diameter of the circle) and height to be 1. This can only be possible if all three vertices lie on the circle not when one is at the centre.
_________________

Click below to check out some great tips and tricks to help you deal with problems on Remainders!
http://gmatclub.com/forum/compilation-of-tips-and-tricks-to-deal-with-remainders-86714.html#p651942

Word Problems Made Easy!
1) Translating the English to Math : http://gmatclub.com/forum/word-problems-made-easy-87346.html
2) 'Work' Problems Made Easy : http://gmatclub.com/forum/work-word-problems-made-easy-87357.html
3) 'Distance/Speed/Time' Word Problems Made Easy : http://gmatclub.com/forum/distance-speed-time-word-problems-made-easy-87481.html

Kudos [?]: 1658 [15], given: 18

Math Expert
Joined: 02 Sep 2009
Posts: 42256

Kudos [?]: 132742 [3], given: 12360

Re: GMAT Prep Triangle/Circle [#permalink]

### Show Tags

06 Dec 2009, 14:15
3
KUDOS
Expert's post
1
This post was
BOOKMARKED
sriharimurthy wrote:
[Note to Bunuel : I think this one might have been missed in the post on triangles?]

This is a useful property, thank you. +1.

For an isosceles triangle with given length of equal sides right triangle (included angle) has the largest area.

And vise-versa:

Right triangle with a given hypotenuse has the largest area when it's an isosceles triangle.
_________________

Kudos [?]: 132742 [3], given: 12360

Manager
Joined: 09 May 2009
Posts: 204

Kudos [?]: 268 [2], given: 13

Re: GMAT Prep Triangle/Circle [#permalink]

### Show Tags

10 Dec 2009, 20:52
2
KUDOS
arjunrampal wrote:
Has anyone got a diagram of the trangle in circle for this question? I'm unable to visualize the diagram from the question

fig attached
Attachments

circle.doc [23.5 KiB]

_________________

GMAT is not a game for losers , and the moment u decide to appear for it u are no more a loser........ITS A BRAIN GAME

Kudos [?]: 268 [2], given: 13

Senior Manager
Joined: 30 Aug 2009
Posts: 283

Kudos [?]: 191 [0], given: 5

Location: India
Concentration: General Management
Re: Maximum Area - No clues [#permalink]

### Show Tags

14 Mar 2010, 02:57
mustdoit wrote:
What is the greatest possible area of a triangular region with one vertex at the center of a circle of radius 1 and the other two vertices on the circle?

a. rt3/4
b. 1/2
c. Pi/4
d. 1
e. rt2

OA:
[Reveal] Spoiler:
B

let the vertex at Centre be A and B and C are vertices of trianle on the circle
so length of side AB and AC will be equal to radius of circle =1.In this case the maximum area will be obtained for a right angled isosceles traiangle

1/2* AB* AC = 1/2 *1*1 = 1/2

Kudos [?]: 191 [0], given: 5

Manager
Joined: 13 Dec 2009
Posts: 248

Kudos [?]: 258 [0], given: 13

Re: Maximum Area - No clues [#permalink]

### Show Tags

14 Mar 2010, 03:20
mustdoit wrote:
What is the greatest possible area of a triangular region with one vertex at the center of a circle of radius 1 and the other two vertices on the circle?

a. rt3/4
b. 1/2
c. Pi/4
d. 1
e. rt2

OA:
[Reveal] Spoiler:
B

Let say b is the third side's length and a is the equal sides' lenght.
then the area of triangle by hero's formula will be b * sqrt(4 a^2 - b^2)/4
putting value of a
=> Area = b * sqrt(4 - b^2)/4
now to get maximum value of Area we have to take derivative of Area in terms of the third side.
For maximum Area its square will also be maximum, that's why squaring both the sides
=> Area^2 = b^2 * (4 - b^2)/16
=> Taking derivative both the sides
=> d(Area^2)/db = (8b-4b^3)/16
equate RHS to 0 to get value of b for which Area is maximum
(8b - 4b^3)/16 = 0
=>2b-b^3 = 0
=>b (2-b^2) = 0
b = 0, |b| = sqrt 2
now b cannot be negative so
b = 0, b = sqrt 2
for these two values sqrt 2 will give the maximum area and put this value in
Area = b * sqrt(4 - b^2)/4

Area = (sqrt 2 * sqrt 2) / 4 = 1/2 hence b is the answer.
_________________

My debrief: done-and-dusted-730-q49-v40

Kudos [?]: 258 [0], given: 13

Manager
Joined: 21 Jan 2010
Posts: 220

Kudos [?]: 105 [1], given: 38

Re: Maximum Area - No clues [#permalink]

### Show Tags

14 Mar 2010, 09:22
1
KUDOS
Can I see it this way?

If you know what is function sin, it has a range from -1 to 1:

Since area of triangle = 1/2 x (side a x side b x sin C), where C is the angle in between side a and b.
The area would be at its maximum when C equals 90 degrees, i.e. sin C = 1.

In this case, we can take side a and side b the radii and C 90 degrees:
1/2 x 1 x 1 x 1 = 1/2

Hope this helps.

Kudos [?]: 105 [1], given: 38

Manager
Joined: 08 Oct 2009
Posts: 64

Kudos [?]: 24 [0], given: 4

Location: Denver, CO
WE 1: IT Business Analyst-Building Materials Industry
Re: Maximum Area of Inscribed Triangle [#permalink]

### Show Tags

06 Apr 2010, 17:49
I got this right on my test, does my thought process make sense?

I know that for a set perimeter of a quadrilateral a square will maximize area, so if you have 16 feet of fence to enclose a garden and want to maximize the area of the garden you would build a square fence around the garden.

EX: Perimeter= 16 Area of square=16
Ex: Perimeter of a rectangle with width of 2 and length of 6=16 Area of the rectangle= 12

So for this problem I thought that a 45-45-90 triangle is half of a square therefore this triangle must maxmize the area with given base.

Sorry if this is confusing, but is this mathmatically correct?

Kudos [?]: 24 [0], given: 4

Senior Manager
Joined: 19 Nov 2009
Posts: 311

Kudos [?]: 99 [0], given: 44

Re: GMAT PREP (PS) [#permalink]

### Show Tags

06 May 2010, 13:13
With one of the vertices at the centre, the two sides of the traingle could be perpendicular to each other (2 radii) and the third side joining the two vertices will be the hypotenuse. Hence, the area will be 1/2 * 1 *1 = 1/2 !
_________________

"Success is going from failure to failure without a loss of enthusiam." - Winston Churchill

As vs Like - Check this link : http://www.grammar-quizzes.com/like-as.html.

Kudos [?]: 99 [0], given: 44

Retired Moderator
Joined: 02 Sep 2010
Posts: 793

Kudos [?]: 1209 [0], given: 25

Location: London
Re: PS question: need help [#permalink]

### Show Tags

23 Oct 2010, 03:38
satishreddy wrote:
ps question

Trignometry based solution

Note that such a triangle is always isosceles, with two sides=1 (the radius of the circle).
Let the third side be b (the base) and the height be h.
If you imagine the angle subtended at the centre by the thrid side, and let this angle be x.

The base would be given by 2*sin(x/2) and the height by cos(x/2); where x is a number between 0 and 180

The area is therefore, sin(z)*cos(z), where z is between 0 and 90.
We can simplify this further as $$sin(z)*\sqrt{1-sin^2(z)}$$, with z between 0 and 90, for which range sin(z) is between 0 and 1.

So the answer is maxima of the function $$f(y)=y*\sqrt{1-y^2}$$ with y between 0 and 1.
This is equivalent to finding the point which will maximize the square of this function $$g(y)=y^2(1-y^2)$$ which is easy to do taking the first derivative, $$g'(y)=2y-4y^3$$, which gives the point as $$y=\frac{1}{\sqrt{2}}$$.

If we plug it into f(y), the answer is area = 0.5 .. Hence answer is (b)

Basically the solution above proves that for an isosceles triangle, when the length of the equal sides is fixed, the area is maximum when the triangle is a right angled triangle ($$y=sin(x/2)=\frac{1}{\sqrt{2}}$$ means x=90). This is a result you will most liekly see being quoted on alternate solutions.
_________________

Kudos [?]: 1209 [0], given: 25

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7738

Kudos [?]: 17808 [1], given: 235

Location: Pune, India
Re: Maximum Area - No clues [#permalink]

### Show Tags

23 Oct 2010, 06:36
1
KUDOS
Expert's post
Interesting Question!
As CalvinHobbes suggested, the easiest way to deal with it might be through the area formula:
Area = (1/2)abSinQ
a and b are the lengths of two sides of the triangle and Q is the included angle between sides a and b.
(It is anyway good to remember this area formula if you are a little comfortable with trigonometry because it could turn your otherwise tricky question into a simple application.)

If we want to maximize area, we need to maximize Sin Q since a and b are already 1.
Maximum value of Sin Q is 1 which happens when Q = 90 degrees.

Therefore, maximum area of the triangle will be (1/2).1.1.1 = (1/2)
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Kudos [?]: 17808 [1], given: 235 Director Joined: 01 Feb 2011 Posts: 725 Kudos [?]: 146 [0], given: 42 Re: Maximum Area - No clues [#permalink] ### Show Tags 11 Jun 2011, 17:59 Area is maximum in an isosceles triangle when angle between two same sides is 90. Maximum area = 1/2 (r)(r) = (1/2) (r^2) = 1/2 Answer is B. Kudos [?]: 146 [0], given: 42 Intern Joined: 05 Aug 2012 Posts: 16 Kudos [?]: 9 [0], given: 8 Location: United States (CO) Concentration: Finance, Economics GMAT Date: 01-15-2014 GPA: 2.62 WE: Research (Investment Banking) Re: What is the greatest possible area of a triangular region [#permalink] ### Show Tags 17 Oct 2013, 18:25 I solved the question the following way.. I gathered the greatest possible triangle has a 90 degree angle where 2 sides meet (each length 1, the radius) This means the 3rd side will be $$\sqrt{2}$$ (90/45/45 rule) It's base will be $$\sqrt{2}$$ and its height will be $$\sqrt{2}$$/$$2$$ So base times height over 2 looks as such- $$\sqrt{2}*\sqrt{2}/2$$ all over 2 which yields 1/2. am I getting the right answer the wrong way? Kudos [?]: 9 [0], given: 8 Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7738 Kudos [?]: 17808 [3], given: 235 Location: Pune, India Re: What is the greatest possible area of a triangular region [#permalink] ### Show Tags 17 Oct 2013, 20:56 3 This post received KUDOS Expert's post bscharm wrote: I solved the question the following way.. I gathered the greatest possible triangle has a 90 degree angle where 2 sides meet (each length 1, the radius) This means the 3rd side will be $$\sqrt{2}$$ (90/45/45 rule) It's base will be $$\sqrt{2}$$ and its height will be $$\sqrt{2}$$/$$2$$ So base times height over 2 looks as such- $$\sqrt{2}*\sqrt{2}/2$$ all over 2 which yields 1/2. am I getting the right answer the wrong way? I think you complicated the question for no reason even though your answer and method, both are correct (though not optimum). The most important part of the question is realizing that the triangle will be a right triangle. Once you did that, you know the two perpendicular sides of the triangle are 1 and 1 (the radii of the circle). The two perpendicular sides can very well be the base and the height. So area = (1/2)*1*1 = 1/2 In fact, this is used sometimes to find the altitude of the right triangle from 90 degree angle to hypotenuse. You equate area obtained from using the perpendicular side lengths with area obtained using hypotenuse. In this question, that will be $$(1/2)*1*1 = (1/2)*\sqrt{2}*Altitude$$ You get altitude from this. How to realize it will be a right triangle without knowing the property: You can do that by imagining the situation in which the area will be minimum. When the two sides overlap (i.e the angle between them is 0), the area will be 0 i.e. there will be no triangle. As you keep moving the sides away from each other, the area will increase till it eventually becomes 0 again when the angle between them is 180. So the maximum area between them will be when the angle between the sides is 90. Attachment: Ques3.jpg [ 22.49 KiB | Viewed 11064 times ] _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

Veritas Prep Reviews

Kudos [?]: 17808 [3], given: 235

Current Student
Joined: 06 Sep 2013
Posts: 1972

Kudos [?]: 741 [0], given: 355

Concentration: Finance
Re: GMAT Prep Triangle/Circle [#permalink]

### Show Tags

25 Apr 2014, 05:51
Bunuel wrote:
What is the greatest possible area of a triangular region with one vertex at the center of a circle of radius one and the other two vertices on the circle?

Clearly two sides of the triangle will be equal to the radius of 1.

Now, fix one of the sides horizontally and consider it to be the base of the triangle.

$$area=\frac{1}{2}*base*height=\frac{1}{2}*1*height=\frac{height}{2}$$.

So, to maximize the area we need to maximize the height. If you visualize it, you'll see that the height will be maximized when it's also equals to the radius thus coincides with the second side (just rotate the other side to see). which means to maximize the area we should have the right triangle with right angle at the center.

$$area=\frac{1}{2}*1*1=\frac{1}{2}$$.

You can also refer to other solutions:
triangular-region-65317.html

Having some trouble figuring out why right isosceles triangle has greater area than equilateral triangle
Anyone would mind clarifying this?

Cheers!
J

Kudos [?]: 741 [0], given: 355

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7738

Kudos [?]: 17808 [0], given: 235

Location: Pune, India
Re: GMAT Prep Triangle/Circle [#permalink]

### Show Tags

27 Apr 2014, 22:39
jlgdr wrote:
Bunuel wrote:
What is the greatest possible area of a triangular region with one vertex at the center of a circle of radius one and the other two vertices on the circle?

Clearly two sides of the triangle will be equal to the radius of 1.

Now, fix one of the sides horizontally and consider it to be the base of the triangle.

$$area=\frac{1}{2}*base*height=\frac{1}{2}*1*height=\frac{height}{2}$$.

So, to maximize the area we need to maximize the height. If you visualize it, you'll see that the height will be maximized when it's also equals to the radius thus coincides with the second side (just rotate the other side to see). which means to maximize the area we should have the right triangle with right angle at the center.

$$area=\frac{1}{2}*1*1=\frac{1}{2}$$.

You can also refer to other solutions:
triangular-region-65317.html

Having some trouble figuring out why right isosceles triangle has greater area than equilateral triangle
Anyone would mind clarifying this?

Cheers!
J

Couple of ways to think about it:

Method 1:
Say base of a triangle is 1.
Area = (1/2)*base*height = (1/2)*height

Say, another side has a fixed length of 1. You start with the first figure on top left when two sides are 1 and third side is very small and keep rotating the side of length 1. The altitude keeps increasing. You get an equilateral triangle whose altitude is $$\sqrt{3}/2 * 1$$ which is less than 1. Then you still keep rotating till you get the altitude as 1 (the other side). Now altitude is max so area is max. This is a right triangle.
When you rotate further still, the altitude will start decreasing again.
Attachment:

Ques3.jpg [ 25.95 KiB | Viewed 10834 times ]

Method 2:

Given in my post above.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for \$199

Veritas Prep Reviews

Kudos [?]: 17808 [0], given: 235

Re: GMAT Prep Triangle/Circle   [#permalink] 27 Apr 2014, 22:39

Go to page    1   2    Next  [ 25 posts ]

Display posts from previous: Sort by

# What is the greatest possible area of a triangular region

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.