a^4-a^3+a^2-a=a^3(a-1)+a(a-1)=a(a-1)(a^2+1)(ax+by)^2+(bx-ay)^2=(ax)^2+2abxy+(by)^2+(bx)^2-2abxy+(ay)^2=(ax)^2+(ay)^2+(by)^2+(bx)^2=a^2(x^2+y^2)+b^2(x^2+y^2)=(x^2+y^2)(a^2+b^2)
(1)A(A2+1)(A-1),其中2为平方(2)题目是不是你写错了