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mandy
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ps 14 Jun 2005, 09:12
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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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ps 14 Jun 2005, 09:53
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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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ps 14 Jun 2005, 11:24
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mandy
. :) 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
Show more


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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ps 14 Jun 2005, 12:42
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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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This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Problem Solving (PS) Forum
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Thank you for understanding, and happy exploring!
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