PQ is a chord of a circle. The tangent XR at X on the circle cuts PQ produced at R. If XR=12 cm, PQ=x cm, QR=x−2 cm, find x (in cm).
According to the tangent – secant theorem the length of tangent squared equals the product of the secant segment and its external segment
⟹PR×QR=RX2
⟹(PQ+QR)×QR=XR2
⟹(x+x−2)(x−2)=144
⟹x2−3x–70=0
(x–10)(x+7)=0
x=10cm