The length of a tangent from a point A at distance 5cm from the centre of the circle is 4cm. Find the radius of the circle.

Given: OA=5cm and AB=4cm
ΔAOB is right angle triangle, right angle at B
By using Pythagoras Theorem, we have
OB² + AB² = OA²
OB is the radius of triangle
OB² + 16 = 25
⇒ OB² = 25 - 16
⇒ OB² = 9
⇒ OB = √9 = 3cm
Radius of circle is 3cm