(a^2-a)^2-(a-1)^2 = [(a^2-a)-(a-1)] [(a^2-a)+(a-1)] = (a^2-a-a+1)(a^2-a+a-1) = (a^2-2a+1)(a^2-1) =(a-1)^2(a-1)(a+1)=(a-1)^3(a+1)
(a+1)(a-1)^3
原式=a^4-a^2-(a^2-1) =a^4-a^2-a^2+1 =a^4-2a^2+1 =(a^2-1)^2……………………………………………………