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rishi2377
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Its A only I guess.
B is a trap.

What say?

-Jack
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all this question is testing the knowlege of isocelese triangles (triangles with two equal angles have two equal sides)

so I have drawn the triangle below. One can deduce from the image that AD=BD=BC




1) gives AD=6, so BC = 6 = SUFFICIENT

2) no information about any dimensions, INSUFFICIENT


ans = A
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This one has to do with remote exterior/interior angles. It's in the gmat supplement, but no matter how many time I memorize the formula I always forget it.
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buffdaddy

so I have drawn the triangle below. One can deduce from the image that AD=BD=BC

That's a mistake. I agree that BD = BC, but you can't assume that AD = BD - it's a very special case for x = 36 degrees. In general x can be 20 degrees or 5 degrees or 40 degrees and then AD != BD.
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maratikus
buffdaddy

so I have drawn the triangle below. One can deduce from the image that AD=BD=BC

That's a mistake. I agree that BD = BC, but you can't assume that AD = BD - it's a very special case for x = 36 degrees. In general x can be 20 degrees or 5 degrees or 40 degrees and then AD != BD.

angle BAD=ABD, AD=BD , doesn't it
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buffdaddy

angle BAD=ABD, AD=BD , doesn't it

I'm sorry, buffdaddy. You are absolutely right. My bad ... (+1)
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maratikus
buffdaddy

angle BAD=ABD, AD=BD , doesn't it

I'm sorry, buffdaddy. You are absolutely right. My bad ... (+1)
no probs mate, for a second u had me real worried though :-D
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Basically the formula read...The measure of an exterior angle of a triangle is equal to the sum of the remote interior angles of the triangle. Hence... BDC = BAD + BDA or 2x = x + y



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