Question

当x=-1,y=-2时，求代数式【2x^2-(x+y)(x-y)】【(-x-y)(-x+y)+2y^2】的值

紧急

Answer 1

这种题目，先化简，再代入求值，这样不会算错
主要考察的化简公式： (x+y)(x-y) = x^2 - y^2
2x^2-(x+y)(x-y)
=2x^2 - (x^2 - y^2)
= x^2 + y^2
= 5

(-x-y)(-x+y)+2y^2
= -(x+y)(y-x) +2y^2
= -(y^2 -x^2) + 2y^2
=x^2 - y^2 + 2y^2
= x^2 + y^2
=5

Answer 2

【2x^2-(x+y)(x-y)】【(-x-y)(-x+y)+2y^2】
=[2x²-(x²-y²)][(x²-y²)+2y²]
=(x²+y²)(x²+y²)
=(x²+y²)²
当x=-1,y=-2时
原式=[（-1)²+(-2)²]²
=(1+4)²
=5²
=25

Answer 3

【2x^2-(x+y)(x-y)】【(-x-y)(-x+y)+2y^2】
=(2x²-x²+y²)(x²-y²+2y²)
=(x²+y²)(x²+y²)
=(x²+y²)²
当x=-1，x=-2时
原式=(1+5)²=36