（a-b+c)(a+b-c)=?(2a-b)^2-(2a+b)^2=?(-x-y)(y-x)+(-x-y)(x+y)=?若a^2+b
问题描述：
（a-b+c)(a+b-c)=?(2a-b)^2-(2a+b)^2=?(-x-y)(y-x)+(-x-y)(x+y)=?若a^2+b
（a-b+c)(a+b-c)=?(2a-b)^2-(2a+b)^2=?(-x-y)(y-x)+(-x-y)(x+y)=?若a^2+b^2.a-b=1.2,求a,b的值
答
(1)(a-b+c)(a+b-c)=[a-(b-c)][a+(b-c)]=a^2-(b-c)^2=a^2-b^2-c^2+2bc(2)(2a-b)^2-(2a+b)^2=(2a-b+2a+b)(2a-b-2a-b)=4a(-2b)=-8ab(3)(-x-y)(y-x)+(-x-y)(x+y)=(x+y)(x-y)-(x+y)^2=x^2-y^2-x^2-2xy-y^2=-2xy-2y^2(4)题...