问题 解答题
巧解密码:
(1)(
4
5
x-10)×
4
5
-12=x-
×
4
5
-12=x-(
2
5
x+10

(2)
x
x+1
-
1
1+x
=
7
8
答案

(1)(

4
5
x-10)×
4
5
-12=x-(
2
5
x+10),

16
25
x-8-12=x-
2
5
x-10,

16
25
x-20=
3
5
x-10,

16
25
x-20+20=
3
5
x-10+20,

16
25
x=
3
5
x+10,

16
25
x-
3
5
x=
3
5
x+10-
3
5
x,

1
25
x=10,

1
25
x×25=10×25,

x=250;

(2)

x
x+1
-
1
x+1
=
7
8

x-1
x+1
=
7
8

8x-8=7x+7,

8x-8+8=7x+7+8,

8x=7x+15,

8x-7x=7x+15-7x,

x=15.

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