Find the length of common chord of two intersecting circles Let us consider two intersection circles 
$x^2+y^2+2g_1x+2f_1y+c_1=0$  
and  $x^2+y^2+2g_2x+2f_2y+c=0$.
Then equation of common chord of the above two circles is
\begin{equation}2(g_1-g_2)x+2(f_1-f_2)y+c_1-c_2=0............(1)
\end{equation}
I want to find the length of the chord (1).
Any one help me to find out the length of chord.
Thank you.

Equation is unnecessary. The length is given by $2\sqrt{(C_1P)^2-(C_1M)^2}$ where $C_1P$ is radius of circle 1 and $C_1M$ is length of perpendicular from $C_1$ to common chord $PQ$ can you take it from there.
