An external point is situated at a distance of 17 cm from the centre of a circle having 16 cm. diameter, let us determine the length of the tangent drawn to the circle from the external point.

Let O be the centre, B be the external point and A be the point where the tangent meets the circle.

OA is the radius of the circle

Diameter = 16 cm

Radius = OA = 8 cm

OB = 17 cm

Δ AOB is a right angled triangle with A = 900

Applying Pythagoras theorem :

AB2 = AO2-OB2

AB2 = 172-82

AB2 = 289-64

AB2 = 225

AB = 15 cm

The length of the tangent drawn to the circle from the external point is 15 cm

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