The question

Find the constants A, B and C for:

$\displaystyle x^2 + 3 = A(x + 1)^2 + B(x - 1)(x + 1) + C(x - 1)$

My attempt

I tried to isolate the constants by substituting strategic values of x. For example:

Let x = -1,

C = -2

Let x = 1,

A = 1

However, I cannot isolate B. I'm sure this question is trivial and my brain is still in holiday mode. Any assistance would be most welcome.