Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 11 Mar 2014, 18:18

### 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

# If you have an equilateral triangle. That triangle is

Author Message
TAGS:
Intern
Joined: 05 Nov 2007
Posts: 36
Followers: 0

Kudos [?]: 2 [0], given: 0

If you have an equilateral triangle. That triangle is [#permalink]  18 Aug 2008, 07:52
If you have an equilateral triangle.
That triangle is enclosed perfectly in a circle such that each corner is exactly touching the edge of the circle.
What is the radius of the circle with relation to one side of the triangle?

Thanks.
SVP
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 27

Kudos [?]: 398 [1] , given: 32

Re: Equilateral Triangle enclosed in a circle [#permalink]  18 Aug 2008, 07:56
1
KUDOS
\frac{1}{3}\sqrt{3}
explanation in a minute...

I think I remember reading somewhere that the center of the circle will be 2/3 from any of the 3 vertices of triangle. So if an equilateral triangle creates 2 30:60:90 triangles back-to-back, then the height of the triangle will be \sqrt{3}, and the radius should be 2/3 of that length. But the question asks for the relation of the radius to any side of the equilateral triangle. The relationship of the "height" of the equilateral triangle to a side is 2:\sqrt{3}. So this would be \frac{2}{3}\sqrt{3}:2 because the radius of the circle to one side of the triangle. This would be the same as dividing \frac{2}{3}\sqrt{3} by 2. so 2/3 * 1/2 = 1/3...or \frac{1}{3}\sqrt{3}. I'm not sure if this is correct, but it seems logical to me.

I think this is correct. see the following link:
_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$. Intern Joined: 05 Nov 2007 Posts: 36 Followers: 0 Kudos [?]: 2 [0], given: 0 Re: Equilateral Triangle enclosed in a circle [#permalink] 18 Aug 2008, 08:47 This makes sense to me too. The link you attached, the images don't appear for me, but I vaguely remember reading that 1/3, 2/3 center point as well. Thanks for the help and quick reply +1 Director Joined: 27 May 2008 Posts: 552 Followers: 5 Kudos [?]: 142 [0], given: 0 Re: Equilateral Triangle enclosed in a circle [#permalink] 18 Aug 2008, 08:56 i think its very useful to memorize some common sin cos and tan values. sin 30 = 1/2, sin 60 = sqrt(3)/2, and 45 = 1/sqrt(2) cos 30 = sqrt(3)/2, cos 60 = 1/2, and cos 45 = 1/sqrt(2) tan 30 = 1/sqrt(3), tan 60 = sqrt(3), and tan 45 = 1 just remember these 6 values ... its easy.. and it helps a lot in geamatry questions... for example all i have to do is hypotneous = r base = a/2 angle = 30 cos 30 = (a/2)/r = sqrt(3)/2 a/r = sqrt(3) SVP Joined: 07 Nov 2007 Posts: 1833 Location: New York Followers: 23 Kudos [?]: 379 [3] , given: 5 Re: Equilateral Triangle enclosed in a circle [#permalink] 18 Aug 2008, 09:07 3 This post received KUDOS gmatatouille wrote: If you have an equilateral triangle. That triangle is enclosed perfectly in a circle such that each corner is exactly touching the edge of the circle. What is the radius of the circle with relation to one side of the triangle? Thanks. Attachments tri-in-circle.gif [ 4.65 KiB | Viewed 1592 times ] _________________ Your attitude determines your altitude Smiling wins more friends than frowning Intern Joined: 17 Aug 2008 Posts: 20 Followers: 0 Kudos [?]: 0 [0], given: 0 Re: Equilateral Triangle enclosed in a circle [#permalink] 18 Aug 2008, 09:43 The triangle can be divided into three equal sectors and their point of intersection will be the center of the circle, which is also the centroid of the triangle. The centroid of a triangle is (2/3)*(height); Height = (side*sqrt[3]/2). This will give us the radius to be side/sqrt[3]. Cheers. SVP Joined: 17 Jun 2008 Posts: 1580 Followers: 8 Kudos [?]: 160 [0], given: 0 Re: Equilateral Triangle enclosed in a circle [#permalink] 19 Aug 2008, 21:43 an arc on circle makes double the angle on the center to what it makes on the opposite side on the circle. With this logic, any of the sides of equilateral triangle will make 120 degree angle at the center of the circle. Now, if I divide the triangle made by two radii and one side of the triangle into two halves, each of the triangles will be 30, 60, 90 and if r is the radius, then the side of triangle will become r multiplied by root 3. SVP Joined: 30 Apr 2008 Posts: 1893 Location: Oklahoma City Schools: Hard Knocks Followers: 27 Kudos [?]: 398 [0], given: 32 Re: Equilateral Triangle enclosed in a circle [#permalink] 20 Aug 2008, 03:57 Attachment: CircleAngle.jpg [ 5.01 KiB | Viewed 1506 times ] Looking at the picture above, does Angle ABC work with this rule? If Angle ABC is 52 degrees, is arc AC 104 degrees even though the angle is not uniform (i.e., isosceles or equilateral). scthakur wrote: an arc on circle makes double the angle on the center to what it makes on the opposite side on the circle. With this logic, any of the sides of equilateral triangle will make 120 degree angle at the center of the circle. Now, if I divide the triangle made by two radii and one side of the triangle into two halves, each of the triangles will be 30, 60, 90 and if r is the radius, then the side of triangle will become r multiplied by root 3. _________________ ------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

CEO
Joined: 29 Aug 2007
Posts: 2504
Followers: 47

Kudos [?]: 444 [0], given: 19

Re: Equilateral Triangle enclosed in a circle [#permalink]  20 Aug 2008, 12:51
gmatatouille wrote:
If you have an equilateral triangle.
That triangle is enclosed perfectly in a circle such that each corner is exactly touching the edge of the circle.
What is the radius of the circle with relation to one side of the triangle?

Thanks.

Equilatral triangle with side a inscribed in a circle has r equal to a/sqrt (3)
_________________
Re: Equilateral Triangle enclosed in a circle   [#permalink] 20 Aug 2008, 12:51
Similar topics Replies Last post
Similar
Topics:
An equilateral triangle is inscribed in a circle. This 3 11 May 2004, 02:47
If an equilateral triangle and a square have the same area, 2 16 Jun 2006, 14:15
Equilateral Triangle.. 3 09 Sep 2006, 19:51
Equilateral triangle? 4 13 Oct 2009, 20:08
2 Equilateral triangle BDF is inscribed in equilateral triangl 8 19 Jun 2010, 07:17
Display posts from previous: Sort by