bài1: thực hiện phép tính

a,\(\frac{1}{\left(1-x\right).\left(2-x\right)}+\frac{2}{\left(2-x\right).\left(3-x\right)}+\frac{3}{\left(1-x\right).\left(x-3\right)}\)

b,\(\frac{x^2}{x+1}+\frac{2x}{^{ }x^2-1}-\frac{1}{1-x}+1\)

c,\(\frac{1}{x^3-x}-\frac{1}{\left(x-1\right).x}+\frac{2}{x^2-1}\)