(1)已知x=2,y=5.求代数式:1-x-yx-2y÷x2-y2x2-4xy+4y2的值.(2)化简求值:(x+2x-2+4x2-4x+4)÷xx-2,其中x=-12.-数学

题目简介

(1)已知x=2,y=5.求代数式:1-x-yx-2y÷x2-y2x2-4xy+4y2的值.(2)化简求值:(x+2x-2+4x2-4x+4)÷xx-2,其中x=-12.-数学

题目详情

(1)已知x=2,y=5.求代数式:1-
x-y
x-2y
÷
x2-y2
x2-4xy+4y2
的值.
(2)化简求值:(
x+2
x-2
+
4
x2-4x+4
x
x-2
,其中x=-
1
2
题型:解答题难度:中档来源:不详

答案

(1)原式=1-class="stub"x-y
x-2y
(x-2y)2
(x-y)(x+y)

=1-class="stub"x-2y
x+y

=class="stub"x+y-x+2y
x+y

=class="stub"3y
x+y

当x=2,y=5时,原式=class="stub"3×5
2+5
=class="stub"15
7

(2)原式=
(x+2)(x-2)+4
(x-2)2
class="stub"x-2
x

=
x2
(x-2)2
class="stub"x-2
x

=class="stub"x
x-2

当x=-class="stub"1
2
时,原式=
-class="stub"1
2
-class="stub"1
2
-2
=class="stub"1
5

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