Let the two points be A and B. Try to apply: \(\displaystyle d(A,B)=2\cdot d(A,M)=2\cdot d(B,M)\).

\(\displaystyle d(A,B)\) is the distance between A and B.

\(\displaystyle d(A,M) \cdot d(M,B) = x(r-x)\:\) , where **x** is the minimal distance between M and the circle .

Now take examples and verify the result you got with a graphing calculator .