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Abhishek009
\(H = \sqrt{12^2 + 9^2}\)

Or, \(H = \sqrt{225}\)

So, \(H = 15\), Answer must be (D)
Abhishek009
I guess its c^2 > a^2 + b^2 for an obtuse triangle, and not c^2 = a^2 + b^2

Please correct me if I am wrong.
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MathRevolution
[Math Revolution GMAT math practice question]

The lengths of two sides of a certain obtuse triangle are \(9\) and \(12\). Which of the following could be the length of the third side of the triangle?

\(A. 12\)
\(B. 13\)
\(C. 14\)
\(D. 15\)
\(E. 16\)

In a right triangle \(a^2+b^2=c^2\) and in an obtuse angle c becomes even bigger so \(a^2+b^2<c^2............9^2+12^2<c^2..........c^2>255\)
So C can be 16....
But say the largest side is 12, then \(9^2+c^2<12^2.....c^2<144-81......c^2<63.......c<8\)

Therefore either c>15 or c<8, hence ONLY 16 fits in...
E
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If a, b and c are sides of a right triangle and c is the longest side, then c^2 = a^2 + b^2.
If a, b and c are sides of an acute triangle and c is the longest side, then c^2 < a^2 + b^2.
If a, b and c are sides of an obtuse triangle and c is the longest side, then c^2 > a^2 + b^2.

Since 15^2 = 9^2 + 12^2 and 16 > 15, 16 could be the third side of the obtuse triangle.

Therefore, the answer is E.

Answer : E
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