先化简,再求值:2(x+y)(-y+x)-(x+y)2+(x-y)2,其中x=2,y=12.-数学

题目简介

先化简,再求值:2(x+y)(-y+x)-(x+y)2+(x-y)2,其中x=2,y=12.-数学

题目详情

先化简,再求值:2(x+y)(-y+x)-(x+y)2+(x-y)2,其中x=2,y=
1
2
题型:解答题难度:中档来源:不详

答案

2(x+y)(-y+x)-(x+y)2+(x-y)2
=2(x+y)(x-y)-(x+y)2+(x-y)2
=2(x2-y2)-x2-2xy-y2+x2-2xy+y2
=2(x2-y2-2xy),
∵x=2,y=class="stub"1
2
.  
∴原式=2×(4-class="stub"1
4
-2)=class="stub"7
2

故答案为class="stub"7
2

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