(A)1a2−b2[atan−1(xa)+btan−1(xb)]+c(B)1a2+b2[atan−1(xa)−btan−1(xb)]+c(C)1a2−b2[atan−1(xa)−btan−1(xb)]+c(D)1a+b[atan−1(xa)−btan−1(xb)]+c