Let O be the center of circle, OP = 29 cm (given)
Radius of a circle = 20 cm
Let T be any point on the circumference of the circle, then PT is the tangent to the circle.
From Figure:
OT is radius and PT is the tangent
This implies, OT ⊥ PT
In right ∆OPT,
By Pythagoras Theorem:
OP2 = OT2 + PT2
(29)2 = (20)2 + PT2
841 = 400 + PT2
PT2 = 441
or PT = 21
Length of tangent PT is 21 cm