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ps

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mandy
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ps [#permalink] ps   14 Jun 2005, 09:12
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A
B
C
D
E

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. :) hello
does anyone has a clue on that one thanks
I found 2x=a+b and y =a-x
(a+b) (a-x) Which does not lead to any answer choices
If x + y = a and x – y = b, then 2xy =
(A) a^2-b^2/2
(B) b^2-b^2/2
(C) a-b/2
(D) ab/2
(E) a^2+b^2/2



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katrin
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Re: ps [#permalink] ps   14 Jun 2005, 09:53
Looks like A:

adding the equations we get:

2x=a+b

sutracting the equations we get:

2y=a-b

multiplying the equations that we've got we get:

4xy=a^2-b^2

so 2xy= a^2-b^2/2
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HowManyToGo
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Re: ps [#permalink] ps   14 Jun 2005, 11:24
mandy wrote:
. :) hello
does anyone has a clue on that one thanks
I found 2x=a+b and y =a-x
(a+b) (a-x) Which does not lead to any answer choices
If x + y = a and x – y = b, then 2xy =
(A) a^2-b^2/2
(B) b^2-b^2/2
(C) a-b/2
(D) ab/2
(E) a^2+b^2/2


yeah 2x = a + b , but since all the choices are expressed in terms of and b , you should express y in terms of a and b.
y = a - b.
Hence A.

HMTG.
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christoph
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Re: ps [#permalink] ps   14 Jun 2005, 12:42
mandy, you forgot the brackets otherwise none of your choices is right. it should be (a^2-b^2)/2. another very fast solution is to pick numbers.



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Re: ps [#permalink]
14 Jun 2005, 12:42
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