Which of the following is correct? a) (a−b)2=a2+2ab−b2 b) (a−b)2=a2−2ab+b2 c) (a−b)2=a2−b2 d) (a+b)2=a2+2ab−b2
The length of common chord of the circles (x−a)2+y2 =a2 and x2+(y−b)2 = b2 is