If equation |x| + |y| = 5 encloses a certain region on the

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If equation |x| + |y| = 5 encloses a certain region on the [#permalink]

18 Jan 2008, 00:38

If equation |x| + |y| = 5 encloses a certain region on the graph, what is the area of that region?

* 5
* 10
* 25
* 50
* 100

i don't even know how to evaluate a statement like that...

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Re: absolute value problem [#permalink]

18 Jan 2008, 00:46

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D

Just draw it.
we have a square with diagonal=5*2=10

Area=a^2=\frac{(\sqrt2*a)^2}{2}=\frac{(diagonal)^2}{2}=\frac{(10)^2}{2}=50

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Re: absolute value problem [#permalink]

18 Jan 2008, 01:06

walker wrote:

D

Just draw it.
we have a square with diagonal=5*2=10

Area=a^2=\frac{(\sqrt2*a)^2}{2}=\frac{(diagonal)^2}{2}=\frac{(10)^2}{2}=50

sweet... kudos +1... check back on the exponent question i had for me.

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Re: absolute value problem [#permalink]

18 Jan 2008, 07:55

my approach was similar to walker's - it's important to draw it to visualize, then obviously the area of each triangle is 5*5/2 = 25/2 and there are 4 triangles. the answer is 50.

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Re: absolute value problem [#permalink]

19 Jan 2008, 02:41

walker wrote:

D

Just draw it.
we have a square with diagonal=5*2=10

Area=a^2=\frac{(\sqrt2*a)^2}{2}=\frac{(diagonal)^2}{2}=\frac{(10)^2}{2}=50

At first, I dont know how to solve this problem, but when I see your drawing, I read it as:

Keep x=0, you had y = + - 5, and vice versa, keep y=0, you had x = +-5.

Do you have any tips for absolute value problem? When problem involves x and y, I am in block.
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Re: absolute value problem [#permalink]

19 Jan 2008, 03:05

sondenso wrote:

Do you have any tips for absolute value problem? When problem involves x and y, I am in block.

The right but long approach is:

|x| + |y| = 5

is equal:

x+y=5\text{ if x\ge0;y\ge0}
x-y=5\text{ if x\ge0;y<0}
-x+y=5\text{ if x<0;y\ge0}
-x-y=5\text{ if x<0;y<0}

shortcut:

your drawing have to be symmetric for x and y. Therefore you can draw only x+y=5 (I quadrant) and use mirror symmetry
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Re: absolute value problem [#permalink]

07 Feb 2008, 01:19

can we take 3,2 or 4,1 as points?
Since the absolute value will always be "5".

-Jack

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Re: absolute value problem [#permalink]

07 Feb 2008, 01:54

jackychamp wrote:

can we take 3,2 or 4,1 as points?
Since the absolute value will always be "5".

-Jack

we can but these points are not vertexs of the square and therefore, the points cannot help us to find area.
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Re: absolute value problem [#permalink] 07 Feb 2008, 01:54

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If equation |x| + |y| = 5 encloses a certain region on the

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