Tìm các số A,B,C để có :
a) \(\frac{x^2-x+2}{\left(x-1\right)^3}\) =\(\frac{A}{\left(x-1\right)^3}\) +\(\frac{B}{\left(x-1\right)^2}\) +\(\frac{C}{x-1}\)
b)\(\frac{x^2+2x-1}{\left(x-1\right)\left(x^2+1\right)}\) =\(\frac{A}{x-1}\) +\(\frac{Bx+C}{x^2+1}\)