ICSE Class 10: Videos

Two parallel tangents PQ and RS touch the circle C at A and B, respectively, then AB is the diameter of the circle. 

Two concentric circles have centre O. A chord PQ of the larger circle is bisected by the smaller circle at point R, so PQ is tangent to the smaller circle. 

By the SSS property of congruence, ∆OPR is congruent to ∆OQR. 

In ∆OBA, 

OA² = OB² + AB²17² = OB² + 8² OB² = 225 OB = 15 cm OB² = 225 - 64

OB² = 225  

OB = 15 cm