分解因式：(x+y)(x-y)-(x+y)² 3m(m-n)+6n(n-m) x(x-y)-y(y-x) (x-3)²+（3x-9)

解1题原式=(x+y)[(x-y)-(x+y)]=(x+y)(x-y-x-y)=(x+y)×(-2y)=-2y(x+y)解2题原式=3m(m-n)-6n(m-n)=3(m-n)(m-2n)解3题原式=x(x-y)+y(x-y)=(x-y)(x+y)解4题原式=(x-3)²+3(x-3)=(x-3)[(x-3)+3]=x(x-3)...