UPSC CDS 2 2018 Math Paper

In the following figure, PO = 6 cm and AT = 4 cm.Radius of a circle is perpendicular to a tangent. Therefore, Δ OTP is a right–angled triangle.
OT = OA + AT = 6 + 4 = 10 cm
PT=√OT2−OP2=√102−62
=√100−36=√64=8cm