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# In the x-y plane the area of the region bounded by the

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In the x-y plane the area of the region bounded by the [#permalink]

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08 Nov 2009, 14:11
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In the x-y plane, the area of the region bounded by the graph of |x+y| + |x-y| = 4 is

A. 8
B 12
C. 16
D. 20
E. 24

Need help in solving equations involving Mod......
help?
[Reveal] Spoiler: OA

Last edited by Bunuel on 15 Feb 2012, 00:29, edited 2 times in total.
Edited the question and added the OA
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08 Nov 2009, 14:34
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papillon86 wrote:
In x-y plane, the area of the region bounded by the graph of |x+y| + |x-y| = 4 is

a) 8
b) 12
c) 16
d) 20

Need help in solving equations involving Mod......
help?

OK, there can be 4 cases:

|x+y| + |x-y| = 4

A. x+y+x-y = 4 --> x=2
B. x+y-x+y = 4 --> y=2
C. -x-y +x-y= 4 --> y=-2
D. -x-y-x+y=4 --> x=-2

The area bounded by 4 graphs x=2, x=-2, y=2, y=-2 will be square with the side of 4 so the area will be 4*4=16.
Attachment:

MSP17971c13h40gd024h6g10000466ge1e9df941i96.gif [ 1.86 KiB | Viewed 10876 times ]

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08 Nov 2009, 17:41
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srini123 wrote:
Thanks Bunuel, I used similar method for a similar question and I got wrong answer
the question was

what is the area bounded by graph$$|x/2| + |y/2| = 5$$?

I got hunderd since
x=10
x=-10
y=10
y=-10

isnt the area 400 ? the answer given was 200, please explain

I think this one is different.

$$|\frac{x}{2}| + |\frac{y}{2}| = 5$$

After solving you'll get equation of four lines:

$$y=-10-x$$
$$y=10+x$$
$$y=10-x$$
$$y=x-10$$

These four lines will also make a square, BUT in this case the diagonal will be 20 so the $$Area=\frac{20*20}{2}=200$$. Or the $$Side= \sqrt{200}$$, area=200.

If you draw these four lines you'll see that the figure (square) which is bounded by them is turned by 90 degrees and has a center at the origin. So the side will not be 20.

Also you made a mistake in solving equation. The red part is not correct. You should have the equations written above.

In our original question when we were solving the equation |x+y| + |x-y| = 4 each time x or y were cancelling out so we get equations of a type x=some value twice and y=some value twice. And these equations give the lines which are parallel to the Y or X axis respectively so the figure bounded by them is a "horizontal" square (in your question it's "diagonal" square).

Hope it's clear.
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13 Dec 2012, 04:06
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eaakbari wrote:
Quote:

OK there can be 4 cases:

|x+y| + |x-y| = 4

A. x+y+x-y = 4 --> x=2
B. x+y-x+y = 4 --> y=2
C. -x-y +x-y= 4 --> y=-2
D. -x-y-x+y=4 --> x=-2

Any absolute values such as |x| = 5 could mean that x = 5 or x = -5.

Derive both (-) and (+) possibilities.

For the problem: |x+y| + |x-y| = 4

We could derive two possibilities for |x+y| could be -(x+y) and (x+y)
We could derive two possibilities for |x-y| could be -(x-y) and (x-y)

This is the reason why we have 4 derived equations.

(x+y) + (x-y) = 4
(x+y) - (x-y) = 4
-(x+y) + (x-y) = 4
-(x+y) - (x-y) = 4

Just simplify those...

If you want more practice on this question type: http://burnoutorbreathe.blogspot.com/2012/12/absolute-values-solving-for-area-of.html
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21 May 2011, 05:46
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|x-y| = x-y if x-y > 0

|x-y| = -(x-y) if x-y < 0

x+y > 0 => x > -y then x !> y

x+y + x - y = 4

x = 2

-x - y + x - y = 4 (if x < -y, then x !< y)

y = -2

x + y -x + y = 4

=> y = 2

-x-y + x - y = 4

=> y = -2

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27 Feb 2012, 23:42
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Expert's post
devinawilliam83 wrote:
Hi,
Can this be solved by graphing. If yes .. how do we graph the equation with 2 mod parts

VeritasPrepKarishma wrote:
VinuPriyaN wrote:
Given |x-y| + |x+y| = 4

I don't understand why can't |x-y| and |x+y| be 1 and 3 instead of 2 and 2! (which again equals 4)

Can any one please explain this to me?

Thanks & Regards,
Vinu

Look at the solution given by Bunuel above. When you solve it, you get four equations.
One of them is x = 2 which means that x = 2 and y can take any value. If y = 1, |x-y| = 1 and |x+y| = 3.
For different values of y, |x-y| and |x+y| will get different values. We are not discounting any of them.

Yes, it can be done by graphing. |x+y| + |x-y| = 4 can expand in four different wasy:

A. x+y+x-y = 4 --> x=2
B. x+y-x+y = 4 --> y=2
C. -x-y +x-y= 4 --> y=-2
D. -x-y-x+y=4 --> x=-2

So you can draw all these four lines x=2, x=-2, y=2, y=-2 to get a square with the side of 4:
Attachment:

Square.gif [ 1.86 KiB | Viewed 15881 times ]
See more examples here:
m06-5-absolute-value-108191.html
graphs-modulus-help-86549.html
m06-q5-72817.html
if-equation-encloses-a-certain-region-110053.html

Hope it helps.
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15 Apr 2014, 05:01
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dheeraj24 wrote:
Yeah karishma,

I totally agree with your explanation, but the point is, why couldn't we draw the slant lines for the points (2,0), (-2,0), (0,2) and (0,-2) instead of horizontal lines and consider the length of diagonal rather than length of side for the original question (|x+y| + |x-y| = 4).

Because you are asked the area of the region bounded by |x+y| + |x-y| = 4.
This equation gives you ONLY horizontal/vertical lines passing through points (2,0), (-2,0), (0,2) and (0,-2) such as x = 2, y = 2, x = -2, y = -2.

Note that x = 2 is the equation of a line (it is not a coordinate) which passes through point (2, 0) and is parallel to the y axis. Similarly, y = 2 is the equation of a line which is parallel to x axis and passes through the point (0, 2) and so on. I think you are taking x = 2 as a coordinate but that is not the case. A coordinate has a value for y too. x =2 is the equation of a line. It implies that x coordinate is always 2 and y can be anything. So all points lying on a line passing through x = 2 and parallel to y axis satisfy this criteria.
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Math Expert Joined: 02 Sep 2009 Posts: 38807 Followers: 7716 Kudos [?]: 105830 [1] , given: 11589 Re: graphs_Modulus....Help [#permalink] ### Show Tags 15 Apr 2014, 09:16 1 This post received KUDOS Expert's post PathFinder007 wrote: Hi Karishma, I am still not clear in question |x/2| + |y/2| = 5 we are getting following cordinates. x=10 x=-10 y=10 y=-10 and in question |x+y| + |x-y| = 4. we are having following cordinates x=2 x=-2 y=2 y=-2 why we are drawing graph differently? Thanks For $$|x+y| + |x-y| = 4$$ the equations are: $$x = 2$$; $$y = 2$$; $$y = -2$$; $$x = -2$$. For $$|\frac{x}{2}| + |\frac{y}{2}| = 5$$ the equations are: $$y=-10-x$$; $$y=10+x$$; $$y=10-x$$; $$y=x-10$$. You might helpful to re-read the thread. _________________ SVP Joined: 08 Jul 2010 Posts: 1630 Location: India GMAT: INSIGHT WE: Education (Education) Followers: 90 Kudos [?]: 1750 [1] , given: 45 Re: In the x-y plane the area of the region bounded by the [#permalink] ### Show Tags 20 Jun 2015, 03:53 1 This post received KUDOS Expert's post jayanthjanardhan wrote: Bunuel wrote: srini123 wrote: Thanks Bunuel, I used similar method for a similar question and I got wrong answer the question was what is the area bounded by graph$$|x/2| + |y/2| = 5$$? I got hunderd since x=10 x=-10 y=10 y=-10 isnt the area 400 ? the answer given was 200, please explain I think this one is different. $$|\frac{x}{2}| + |\frac{y}{2}| = 5$$ After solving you'll get equation of four lines: $$y=-10-x$$ $$y=10+x$$ $$y=10-x$$ $$y=x-10$$ These four lines will also make a square, BUT in this case the diagonal will be 20 so the $$Area=\frac{20*20}{2}=200$$. Or the $$Side= \sqrt{200}$$, area=200. If you draw these four lines you'll see that the figure (square) which is bounded by them is turned by 90 degrees and has a center at the origin. So the side will not be 20. Also you made a mistake in solving equation. The red part is not correct. You should have the equations written above. In our original question when we were solving the equation |x+y| + |x-y| = 4 each time x or y were cancelling out so we get equations of a type x=some value twice and y=some value twice. And these equations give the lines which are parallel to the Y or X axis respectively so the figure bounded by them is a "horizontal" square (in your question it's "diagonal" square). Hope it's clear. Hi bunnel, How did u rhombus for this one and a square for the other one?...I got the limits for both the questions, but could not figure out they turn out to be a square and rhombus!... Even that is a square but never forget that A Square is a specific type of Rhombus only I hope, You can understand that the Product of the slopes of the adjacent sides is -1 in that figure which proves the angle between the adjacent sides as 90 degree a Square is a "Rhombus with all angles 90 degrees". So calling it a Rhombus won't be wrong either but you are right about the figure being a Square. _________________ Prosper!!! GMATinsight Bhoopendra Singh and Dr.Sushma Jha e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772 Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi http://www.GMATinsight.com/testimonials.html 22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION Manager Joined: 15 May 2010 Posts: 186 Location: India Concentration: Strategy, General Management WE: Engineering (Manufacturing) Followers: 0 Kudos [?]: 33 [1] , given: 65 Re: In the x-y plane the area of the region bounded by the [#permalink] ### Show Tags 08 Apr 2016, 12:40 1 This post received KUDOS Bunnel, why the point can't be connected as triangle. x=2, y=2--> what i understood is perpendicular to both the axis. so , it will be square. Am I right? Bunuel wrote: papillon86 wrote: In x-y plane, the area of the region bounded by the graph of |x+y| + |x-y| = 4 is a) 8 b) 12 c) 16 d) 20 Need help in solving equations involving Mod...... help? OK, there can be 4 cases: |x+y| + |x-y| = 4 A. x+y+x-y = 4 --> x=2 B. x+y-x+y = 4 --> y=2 C. -x-y +x-y= 4 --> y=-2 D. -x-y-x+y=4 --> x=-2 The area bounded by 4 graphs x=2, x=-2, y=2, y=-2 will be square with the side of 4 so the area will be 4*4=16. Attachment: MSP17971c13h40gd024h6g10000466ge1e9df941i96.gif Answer: C Senior Manager Affiliations: PMP Joined: 13 Oct 2009 Posts: 305 Followers: 4 Kudos [?]: 168 [0], given: 37 Re: graphs_Modulus....Help [#permalink] ### Show Tags 08 Nov 2009, 15:27 Bunuel wrote: papillon86 wrote: In x-y plane, the area of the region bounded by the graph of |x+y| + |x-y| = 4 is a) 8 b) 12 c) 16 d) 20 Need help in solving equations involving Mod...... help? I've never seen such kind of question in GMAT before. OK there can be 4 cases: |x+y| + |x-y| = 4 A. x+y+x-y = 4 --> x=2 B. x+y-x+y = 4 --> y=2 C. -x-y +x-y= 4 --> y=-2 D. -x-y-x+y=4 --> x=-2 The area bounded by 4 graphs x=2, x=-2, y=2, y=-2 will be square with the side of 4 so the area will be 4*4=16. Answer: C Why cant we consider (4,0) and (0,4) as points on graph ? then area would be different... , right? _________________ Thanks, Sri ------------------------------- keep uppp...ing the tempo... Press +1 Kudos, if you think my post gave u a tiny tip Math Expert Joined: 02 Sep 2009 Posts: 38807 Followers: 7716 Kudos [?]: 105830 [0], given: 11589 Re: graphs_Modulus....Help [#permalink] ### Show Tags 08 Nov 2009, 15:39 srini123 wrote: Why cant we consider (4,0) and (0,4) as points on graph ? then area would be different... , right? First of all we are not considering points separately, as we have X-Y plane and roots of equation will represent lines, we'll get the figure bounded by this 4 lines. The equations for the lines are: x=2 x=-2 y=2 y=-2 This lines will make a square with the side 4, hence area 4*4=16. Second: points (4,0) or (0,4) doesn't work for |x+y| + |x-y| = 4. _________________ Senior Manager Affiliations: PMP Joined: 13 Oct 2009 Posts: 305 Followers: 4 Kudos [?]: 168 [0], given: 37 Re: graphs_Modulus....Help [#permalink] ### Show Tags 08 Nov 2009, 16:58 Bunuel wrote: srini123 wrote: Why cant we consider (4,0) and (0,4) as points on graph ? then area would be different... , right? First of all we are not considering points separately, as we have X-Y plane and roots of equation will represent lines, we'll get the figure bounded by this 4 lines. The equations for the lines are: x=2 x=-2 y=2 y=-2 This lines will make a square with the side 4, hence area 4*4=16. Second: points (4,0) or (0,4) doesn't work for |x+y| + |x-y| = 4. Thanks Bunuel, I used similar method for a similar question and I got wrong answer the question was what is the area bounded by graph$$|x/2| + |y/2| = 5$$? I got hunderd since x=10 x=-10 y=10 y=-10 isnt the area 400 ? the answer given was 200, please explain _________________ Thanks, Sri ------------------------------- keep uppp...ing the tempo... Press +1 Kudos, if you think my post gave u a tiny tip Senior Manager Affiliations: PMP Joined: 13 Oct 2009 Posts: 305 Followers: 4 Kudos [?]: 168 [0], given: 37 Re: graphs_Modulus....Help [#permalink] ### Show Tags 08 Nov 2009, 20:23 Thanks Bunuel , once again wonderful explanation +1 Kudos.. have a good day... _________________ Thanks, Sri ------------------------------- keep uppp...ing the tempo... Press +1 Kudos, if you think my post gave u a tiny tip Senior Manager Joined: 24 Mar 2011 Posts: 450 Location: Texas Followers: 5 Kudos [?]: 183 [0], given: 20 Re: graphs_Modulus....Help [#permalink] ### Show Tags 20 May 2011, 12:39 Bunuel wrote: x=2 x=-2 y=2 y=-2 This lines will make a square with the side 4, hence area 4*4=16. i am still now able to follow if the area that is formed with these lines is as per fig 1 or fig 2 Attachments Doc2.docx [11.23 KiB] Downloaded 135 times  To download please login or register as a user Director Joined: 01 Feb 2011 Posts: 755 Followers: 14 Kudos [?]: 124 [0], given: 42 Re: graphs_Modulus....Help [#permalink] ### Show Tags 20 May 2011, 17:31 Thats same as what you see in fig 2 . agdimple333 wrote: Bunuel wrote: x=2 x=-2 y=2 y=-2 This lines will make a square with the side 4, hence area 4*4=16. i am still now able to follow if the area that is formed with these lines is as per fig 1 or fig 2 Director Joined: 01 Feb 2011 Posts: 755 Followers: 14 Kudos [?]: 124 [0], given: 42 Re: graphs_Modulus....Help [#permalink] ### Show Tags 20 May 2011, 17:33 solving the inequality we have the following as solutions x=2 y=2 y=-2 x=-2 drawing this in a graph, we can observe that it forms a square with side length of 4. Hence the area is 4*4 = 16 Answer is C. VP Status: There is always something new !! Affiliations: PMI,QAI Global,eXampleCG Joined: 08 May 2009 Posts: 1335 Followers: 17 Kudos [?]: 254 [0], given: 10 Re: graphs_Modulus....Help [#permalink] ### Show Tags 20 May 2011, 21:50 so check for ++, +-, -+ and -- giving x=2|-2 and y=2|-2 hence a square with 4*4 area = 16 _________________ Visit -- http://www.sustainable-sphere.com/ Promote Green Business,Sustainable Living and Green Earth !! Intern Joined: 22 May 2011 Posts: 1 Followers: 0 Kudos [?]: 0 [0], given: 0 Re: graphs_Modulus....Help [#permalink] ### Show Tags 22 May 2011, 07:21 Given |x-y| + |x+y| = 4 I don't understand why can't |x-y| and |x+y| be 1 and 3 instead of 2 and 2! (which again equals 4) Can any one please explain this to me? Thanks & Regards, Vinu Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7368 Location: Pune, India Followers: 2281 Kudos [?]: 15079 [0], given: 224 Re: graphs_Modulus....Help [#permalink] ### Show Tags 22 May 2011, 08:38 VinuPriyaN wrote: Given |x-y| + |x+y| = 4 I don't understand why can't |x-y| and |x+y| be 1 and 3 instead of 2 and 2! (which again equals 4) Can any one please explain this to me? Thanks & Regards, Vinu Look at the solution given by Bunuel above. When you solve it, you get four equations. One of them is x = 2 which means that x = 2 and y can take any value. If y = 1, |x-y| = 1 and |x+y| = 3. For different values of y, |x-y| and |x+y| will get different values. We are not discounting any of them. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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