Problem
GEO-B2-M10-P001 A Tangent and a Secant
#1
★★☆☆☆ Level 2 of 5
From point \(P\), a tangent \(PT\) and a secant \(PAB\) are drawn to a circle. Given \(PA=5\), \(PT=10\), find \(PB\).
Use \(PT^2=PA\cdot PB\).
By power of a point, \(PT^2=PA\cdot PB\). Hence \(100=5\cdot PB\), so \(PB=20\).
A warm-up on recognising power of a point.