问题 解答题
解方程.
(1)
5
8
x+2x=
3
4

(2)x+
7
9
x=
2
3
×
1
2

(3)
5
9
x-
3
4
=
1
4

(4)
5
7
x-
2
7
x=42
答案

(1)

5
8
x+2x=
3
4

5
8
+2)x=
3
4

21
8
x=
3
4

21
8
21
8
=
3
4
÷
21
8

x=

2
7

(2)x+

7
9
x=
2
3
×
1
2

(1+

7
9
)x=
1
3

16
9
x=
1
3

16
9
16
9
=
1
3
÷
16
9

x=

3
16

(3)

5
9
X-
3
4
=
1
4

5
9
X-
3
4
+
3
4
=
1
4
+
3
4

5
9
X=1

5
9
5
9
=1÷
5
9

X=

9
5

(4)

5
7
X+
2
7
X=42

5
7
+
2
7
)X=42

X=42

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