计算（a^4-81）/（9+a^2）/(3-a)计算[(x^2+1)^2-4x(x^2+1)4x^2]/(x-1)^2已知x-y=1,xy=2,求x^4y^2-2x^3y^3+x^2y^4的值

Question

计算（a^4-81）/（9+a^2）/(3-a)
计算 [(x^2+1)^2-4x(x^2+1)4x^2]/(x-1)^2
已知x-y=1,xy=2,求x^4y^2-2x^3y^3+x^2y^4的值

Answer 1

（a^4-81）/（9+a^2）/(3-a)=(a^2+9)(a^2-9)/（9+a^2)/(3-a)=(a^2-9)/(3-a)=(a+3)(a-3)/(3-a)= -(a+3)x^4y^2-2x^3y^3+x^2y^4=(yx^2)^2 - 2* yx^2 *xy^2 + (xy^2)^2 = (yx^2 - xy^2)^2 = (xy(x -y))^2 =4