因式分解(x+y)^2
要过程
(x+y)^2-4(x-y)^2-4(x^2-y^2) =(x+y-2x+2y)(x+y+2x-2y)-4(x^2-y^2) =(3y-x)(3x-y)-4(x^2-y^2) =9xy-3x^2-3y^2+xy-4x^2+4y^2 =y^2+10xy-7x^2 =[y+(-5+4√2)x,y+(-5-4√2)x]