Question

In an acute angled triangle PQR,angle PQR=45 degree.Prove that (PR)2=(PQ)2+(QR)2-4ar(trianglePQR).

Answer 1

According to question
Angle PQR = 45 deg

Thus 
Angle PRQ = 2 * Angle PQR       
                   =  90 deg

Thus
According to pythagoras theorem

In triangle PQR
PR^2 = PQ^2 + QR^2