The equation of the two circles are, x2+y2+2x+4y−20=0 x2+y2+6x−8y+10=0 This implies, 2g1g2+2f1f2=6−16 =−10 =c1+c2 The circle intersects orthogonally so have a common tangent. Now the equation of common chord is, 2x−6y+15=0 So, the length of common chord is, 2√25−