计算1.(x+y)(x-y)+(y-z)(y+z)+(z-x)(z+x) 2.（a+b-3)(a+b+3)

题目

计算1.(x+y)(x-y)+(y-z)(y+z)+(z-x)(z+x) 2.（a+b-3)(a+b+3)

答案

1.(x+y)(x-y)+(y-z)(y+z)+(z-x)(z+x)
=x²-y²+y²-z²+z²-x²
=0
2.（a+b-3)(a+b+3)
=(a+b)²-9
=a²+2ab+b²-9