Solution:
Given that length of tangent is 20cm and radius of the circle is 12cm.Therefore, ∠CDP = 90°.
In ∆CDP, By Pythagoras theorem,
Hence, the length of the tangent from an external point P is 16cm.
Therefore, option 3 is correct.
Find the length of the tangent from an external point at a distance of from the centre of a circle of radius 12 cm.