计算:(1)2(m+1)2-(2m+1)(2m-1);(2)4x2-(2x+3)(2x-3);(3)先化简,再求值.[(x+2y)2-(x+y)(3x-y)-5y2]÷2x,其中x=-2,y=12.-

题目简介

计算:(1)2(m+1)2-(2m+1)(2m-1);(2)4x2-(2x+3)(2x-3);(3)先化简,再求值.[(x+2y)2-(x+y)(3x-y)-5y2]÷2x,其中x=-2,y=12.-

题目详情

计算:
(1)2(m+1)2-(2m+1)(2m-1);
(2)4x2-(2x+3)(2x-3);
(3)先化简,再求值.[(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)2(m+1)2-(2m+1)(2m-1),
=2(m2+2m+1)-4m2+1,
=-2m2+4m+3;

(2)4x2-(2x+3)(2x-3),
=4x2-(4x2-9),
=9;

(3)[(x+2y)2-(x+y)(3x-y)-5y2]÷2x
=[(x2+4xy+4y2)-3x2-2xy+y2-5y2]÷2x
=(-2x2+2xy)÷2x
=-x+y,
当x=-2,y=class="stub"1
2
时,原式=-(-2)+class="stub"1
2
=class="stub"5
2

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