（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

（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
（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

（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
(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)题目写漏了?若a^2+b^2?.a^2+b^2=什么?

(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题不会！