Let O be the center of the given circle.
Let P be a point, such that
OP = 17 cm.
Let OT be the radius, where
OT = 5cm
Join TP, where TP is a tangent.
Now, tangent drawn from an external point is perpendicular to the radius at the point of contact.
\(\therefore OT\perp PT\)
In the right \(\triangle OTP,\) we have:
∴ The length of the tangent is 15 cm.