When a = - 1, the fraction a ^ 2-1 / A ^ 2 + 1, a equals 0, B equals 1, C equals - 1, D is meaningless

When a = - 1, the fraction a ^ 2-1 / A ^ 2 + 1, a equals 0, B equals 1, C equals - 1, D is meaningless

Numerator = 0, denominator = 2, choose a