As ΔPQR is right angled at R, then,
PQ2=QR2+PR2
Since the triangle is an isosceles triangle, then, QR=PR, therefore,
PQ2=PR2+PR2
PQ2=2PR2
Hence proved.
In a triangle PQR right angled at Q if QS = SR then prove that PR2 = 4PS2 - PQ2
ABC is an isosceles triangle right angled at C. Prove that AB2=2AC2