a^4-1/a^2+2a+1:a^2+1/2a+2

(a^4-1)/(a²+2a+1):(a²+1)/(2a+2)=(a²-1)(a²+1)/(a+1)² *2(a+1)/(a²+1)=
=2(a-1)(a+1)/(a+1)²=2(a-1)/(a+1)