(1)因式分解 （x²-y²)-(x+y)²-4(x-y)²
原式=(x+y)(x-y)-(x+y)²-4(x-y)²=(x+y)(x-y-x-y)-4(x-y)²=-2y(x+y)-4(x-y)²
=-2xy+2y²-(4x²-8xy+4y²)=-4x²+6xy-2y²=-2(2x²-3xy+y²)=-2(2x-y)(x-y)
(2)已知x=75/22,y=40/25,计算-6x²+（-5x）-(12x²)+4x
-6x²+（-5x）-(12x²)+4x=-18x²-x=-x(18x+1)=-(75/22)(18×75/22+1)=-(75/22)×(1372/22)
=-102900/484=-25725/121