(1)先化简、再求值:12x-1x+y(x2-y2+x+y2x),其中x=2,y=3.(2)先化简、再求值:a-32a-4÷(5a-2-a-2),其中a=3-3.-数学

题目简介

(1)先化简、再求值:12x-1x+y(x2-y2+x+y2x),其中x=2,y=3.(2)先化简、再求值:a-32a-4÷(5a-2-a-2),其中a=3-3.-数学

题目详情

(1)先化简、再求值:
1
2x
-
1
x+y
(x2-y2+
x+y
2x
)
,其中x=
2
,y=3.
(2)先化简、再求值:
a-3
2a-4
÷(
5
a-2
-a-2)
,其中a=
3
-3
题型:解答题难度:中档来源:不详

答案

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

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

=-(x-y)
=y-x,
当x=
2
,y=3时,
原式=3-
2

(2)原式=class="stub"a-3
2(a-2)
÷[
5-(a+2)(a-2)
(a-2)
]

=class="stub"a-3
2(a-2)
•class="stub"a-2
9-a2

=class="stub"a-3
2(a-2)
•class="stub"a-2
(3+a)(3-a)

=-class="stub"1
2(a+3)

当a=
3
-3时,原式=-class="stub"1
2(
3
-3+3)
=-
3
6

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