1.(a-2b+c)(a+2b-c)-(a+b+c)∧2=-5b^2-2c^2-2ab+2bc-2ac
2.(x-y)(x+y)(x∧2+y∧2)(x∧4+y∧4)
=x^8-y^8
3.求（2x∧5-4x∧4-3x∧3+7x∧2-x-6)(3x∧7-2x∧5-5x∧4+2x∧3+x∧2-2x+1)中x∧9的系数
系数是19
4.若a∧2+b∧2+c∧2=ab+bc+ca,求证a=b=c
证明：方程两边同时乘以2,得2a∧2+2b∧2+2c∧2=2ab+2bc+2ca
右边移项得（a-b）^2+(b-c)^2+(a-c)^2=0
所以a=b=c
5.(x+y)∧4(x-y)∧4
=4[(x^2+y^2)]^4