`A=\frac{a^4-a^2+2a+2}{a^4+a^3+a+1}` ĐKXĐ: $a\neq-1$
`A=\frac{a^2(a^2-1)+2(a+1)}{a^3(a+1)+(a+1)}`
`A=\frac{a^2(a-1)(a+1)+2(a+1)}{(a+1)(a^3+1)}`
`A=\frac{(a+1)[a^2(a-1)+2]}{(a+1)(a^3+1)}`
`A=\frac{(a+1)(a^3-a^2+2)}{(a+1)(a^3+1)}`
`A=\frac{a^3-a^2+2}{a^3+1}`