Two equal circles of radius r intersect such that each passes through the centre of the other. Find the length of the common chord.

Answer 1

Draw a diagram. Note that you have a right triangle with one leg r/2 and hypotenuse r.

Answer 2

Two equal circles of radius r intersect such that each passes through the centre of the other.The length of the common chord of the circle is 13 by 2 r