There are numbers A and B for which A/(x - 1) + B/(x + 1) = (x + 3)/(x^2 - 1) for every number x other than 1 and -1. Find .A - B.
Note x^2 - 1 = (x -1) (x + 1)
( x + 3) / ( x^2 - 1) = A / ( x - 1) + B / ( x + 1) multiply through by ( x - 1) ( x + 1)
x + 3 = A(x + 1) + B (x - 1)
x + 3 = (A + B)x + (A - B)
Equating terms .......this implies that A - B = 3