If the roots of the quadratic equation : p(q-r)x^2+q(r-p)x+r(p-q)=0 are equal show that 1/p+1/r=2/q

Aconstruction worker needs to put a rectangular window in the side of a building he knows from measuring that the top and bottom of the window have a width of 8bfeet and the sides have a length of 15 feet he also measured one diagonal to be 17 feet what is the length of the other diagonal