Question

Find the length of a tangent drawn to a circle of radius 3 cm from a point distant 5cm from the circle

Answer 1

We know tangent to a radius of the circle is perpendicular 
So, angle OAB=90degree
So by pythagoras theorem,
OB square=OAsquare+ABsquare

Answer 2

A tangent is always perpendicular to the radius
ByapplyingPythagorusTheorem
$length \: of \: tangent \\ = \sqrt{ {(5)}^{2} - {(3)}^{2} } \\ = \sqrt{25 - 9} \\ = \sqrt{16 } \\ = 4 \: cm$
so 4 cm is the right answer