Two circles have their centers 21 cm apart. The radii of the circles are 10 cm and 17 cm. Find the length (in cm) of the common chord of the two circles.

 if two circles having radii a and b with the distance between them as c,
Length of common chord= 2* Sqrt [ a^2 - ((a^2+c^2-b^2)/2c)^2]

Ans. 84