If the curves x2a+y2b=1 and  x2c+y2d=1intersect each other at an angle of  90°then which of the following relations is TRUE

The given curves   x2a+y2b=1,x2c+y2d=1intersect orthogonallyThe condition that the curves px2+qy2=1,   p1x2+q1y2=1cuts orthogonally is 1p−1q=1p'−1q'Hence, the required condition is a−b=c−d