Question:
AP and PQ are tangents drawn from a point A to a circle with centre O and radius 9 cm. If OA = 15 cm, then AP + AQ =
(a) 12 cm
(b) 18 cm
(c) 24 cm
(d) 36 cm
Solution:
Let us first put the given data in the form of a diagram.
We know that the radius of the circle will always be perpendicular to the tangent at the point of contact. Therefore,
$O P \perp A P$
$A P^{2}=O A^{2}-O P^{2}$
$A P^{2}=15^{2}-9^{2}$
$A P^{2}=225-81$
$A P^{2}=144$
$A P=\sqrt{144}$
$A P=12$
Since tangents drawn from an external point will be equal in length,
AP = AQ
Since, AP = 12
AQ = 12
AP + AQ = 12 + 12
AP + AQ = 24
Therefore option (c) is the correct answer to this question.