Barrons AP Calculus - David Bock

6. (A) Assume that

Then

2 x^2 − x + 4 = A(x − 1)(x − 2) + Bx(x − 2) + Cx(x − 1).

Since you are looking for B, let x = 1:

2(1) − 1 + 4 = 0 + B(−1) + 0; B = −5.