Two concentric circles are of radii 7 cm and 'r' cm respectively, where r >7 .A chord of the larger circle, of length 48 cm, touches the smaller circle. Find the value of 'r' ?

Let O be the centre of the concentric circles. AB is the chord of the larger circle and tangent to the smaller circle at D.

Given, OD = 7 cm, OB = *r* cm and AB = 48 cm

AB is the tangent to the smaller circle.

∴ ∠ODB = 90° (Radius is perpendicular to the tangent at point of contact)

OD⊥AB,

In ΔODB,

OB^{2} = OD^{2} + BD^{2}

Thus, the value of *r* is 25 cm.

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