Circles

From a point Q, the length of the tangent to a circle is 40cm and the distance Q from the centre is 41cm.Find the radius of the circle.

Sol:       Use phythogoras theorem

         ( OQ )2 =( OP )2+( PQ)2

         ( 41)2 = (OP )2 + (40 )2

         1681 = (OP )2 + 1600

          1681-1600 =( OP )2

            81 = (OP )2.    

            √81 = (OP )2

             9 = (OP )2

              The radius of the circle is 9cm