YLL討論網

1-X平方-Y平方+X平方Y平方

1-x^2-y^2+X^2y^2
=x^2(y^2-1)-(y^2-1)
=(y^2-1))-(x^2-1)
=(y=1)(y-1)(x+1)(x-1)

亡者 寫到:1-X平方-Y平方+X平方Y平方

1-x^2-y^2+x^2 y^2
=(1-x^2)-y^2(1-x^2)<---grouping terms and taking out y as common factor
=(1-x^2)(1-y^2)<---taking out (1-x^2) as common factor
=(1+x)(1-x)(1+y)(1-y)<---using the indentity a^2-b^2=(a+b)(a-b)