Posted by can u do it???? on .
Triangle ABC is a right triangle with ∠ABC=90∘. P is a point within triangle ABC such that ∠APB=∠BPC=∠CPA=120∘. If PA=15 and PB=6, what is the value of PC?

geometry(triangle) 
Steve,
There's probably a good geometric way to do it, but here's a trig way, using the law of cosines.
AB^2 = 6^2+15^2  2 * 6 * 15 * (1/2) = 351
AC^2 = PC^2 + 15^2  2*PC*15(1/2)
BC^2 = PC^2 + 6^2  2*PC*6(1/2)
AC^2BC^2 = AB^2 = 351, so
351 = 189 + 9PC
9PC = 162