a: ĐKXĐ: \(x\notin\left\{1;-1\right\}\)
\(C=\dfrac{x^2+2+x^2-1-x^2-x-1}{\left(x-1\right)\left(x^2+x+1\right)}\cdot\dfrac{x^2+x+1}{\left(x+1\right)\left(x^2-x+1\right)}\)
\(=\dfrac{x^2-x}{\left(x-1\right)}\cdot\dfrac{1}{\left(x+1\right)\left(x^2-x+1\right)}\)
\(=\dfrac{x}{x^3+1}\)
b: |x+1|=2
=>x+1=2 hoặc x+1=-2
=>x=1(loại) hoặc x=-3(nhận)
Thay x=-3 vào C, ta được:
\(C=\dfrac{-3}{-27+1}=\dfrac{-3}{-26}=\dfrac{3}{26}\)