Q11 of 31 Page 218

A tangent drawn to a circle with centre O from an external point A touches the circle at the point B. If OB = 5cm, AO = 13cm, then the length of AB is

The ΔABO formed by joining the three points is always a right angled triangle


AO is the hypotenuse of Δ ABO


Applying Pythagoras theorem :


AB2 = AO2-OB2


⇒ AB2 = 132-52


⇒ AB2 = 169-25


⇒ AB2 = 144


⇒ AB = 12 cm.


So Correct Option is (A)

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