Problem Solving - Why doesn't Picking Numbers Work?

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From Kaplan CAT #2.

If an isoceles right triangle has an area of 2x^2 + 2x + 1/2, what is the Perimeter?
A. 3 (x+1)
B. (2^1/2)(x^2+1)
C. (2x-1)(2x+1)
D. (2+2^1/2)(2x+1)
E. 2x + 2^1/2

This was my approach. Why doesn't picking numbers work here?

2x^2 + 2x + 1/2 = (h*b)/2
Pick x=2
8 + 4 + 0.5 = bh/2
12.5 = bh/2
25 = bh
But triangle is isoceles, so b=h
25 = b^2
So b = 5

If b=5, P = 5+ 5+ 5 (2^0.5)
P = 10 + 5(2^0.5)

If I plug, x=2 into all the answer choices, I should find the equivalent of 10 + 5(2^0.5) among the choices.

Where have I gone wrong?

Please let me know.

Thanks
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by Ian Stewart » Sat Sep 18, 2010 7:20 am
Looks correct to me. Plug x=2 into answer choice D and simplify, and you will find it is equal to the value that you got as your answer.
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by skalevar » Sat Sep 18, 2010 7:27 am
arrg. Stupid Mistake. I was plugging in b=5.

Thanks.