化简求值(1)(x+2)2-(x+1)(x-1),其中x=12;(2)[(xy+2)(xy-2)-2x2y2+4]÷xy,其中x=4,y=12;(3)[(x+2y)2-(x+y)(3x-y)-5y2]

题目简介

化简求值(1)(x+2)2-(x+1)(x-1),其中x=12;(2)[(xy+2)(xy-2)-2x2y2+4]÷xy,其中x=4,y=12;(3)[(x+2y)2-(x+y)(3x-y)-5y2]

题目详情

化简求值
(1)(x+2)2-(x+1)(x-1),其中x=
1
2

(2)[(xy+2)(xy-2)-2x2y2+4]÷xy,其中x=4,y=
1
2

(3)[(x+2y)2-(x+y)(3x-y)-5y2]÷2x,其中x=-2,y=
1
2
题型:解答题难度:中档来源:不详

答案

(1)原式=x2+4x+4-x2+1=4x+5,
当x=class="stub"1
2
时,原式=4×class="stub"1
2
+5=2+5=7;
(2)原式=(x2y2-4-2x2y2+4)÷xy=(-x2y2)÷xy=-xy,
当x=4,y=class="stub"1
2
时,原式=-4×class="stub"1
2
=-2;
(3)原式=(x2+4xy+4y2-3x2+xy-3xy+y2-5y2)÷2x=(-2x2+2xy)÷2x=-x+y,
当x=-2,y=class="stub"1
2
时,原式=2+class="stub"1
2
=2class="stub"1
2

更多内容推荐