试题

题目:
已知x-y+5xy=0,求
-3xy-2(x+y)+4x
-y-2xy+x
的值.
答案
解:∵x-y+5xy=0,
∴x-y=-5xy,
-3xy-2(x+y)+4x
-y-2xy+x

=
-3xy+2(x-y)
-2xy+x-y

=
-3xy+2(-5xy)
-2xy-5xy

=
13
7

解:∵x-y+5xy=0,
∴x-y=-5xy,
-3xy-2(x+y)+4x
-y-2xy+x

=
-3xy+2(x-y)
-2xy+x-y

=
-3xy+2(-5xy)
-2xy-5xy

=
13
7
考点梳理
代数式求值.
先求出x-y,然后整体代入进行计算即可得解.
本题考查了代数式求值,整体思想的利用是解题的关键.
整体思想.
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