math f.2~急!!!

1.
1/3x+2/3x
=1/x

2.
-1/3x-4/3x
=-5/3x

3.
2/(3x-2)-6/(2-3x)
=2/(3x-2)+6/(3x-2)
=8/(3x-2)

4.
2/(4x+1)-6/(-4x-1)
=2/(4x+1)+6/(4x+1)
=8/(4x+1)

5.
4x/9y-1/3y
=4x/9y-3/9y
=(4x-3)/9y

6.
1/3(r+1)-2/6(1+r)
=2/6(r+1)-2/6(1+r)
=0

7.
y/3(4y-9)-3/4(4y-9)
=4y/12(4y-9)-9/12(4y-9)
=(4y-9)/12(4y-9)
=1/12

8.
3/3a
=1/a

9.
5b^2/10b
=b/2

10.
4p/8pq
=1/2q

11.
-3x^2y/6y^2
=-x^2/2y

12.
2/4x-2y
=1/2x-y

13.
y-1/4y-4
=1/4

14.
2a/3b*b
=2a/3

15.
b/4*6a/ab
=3/2

16.
7a/5b*b/a^2
=7/5a

2012-08-15 12:15:42 補充：
回答kyle的問題：
他(tze ching)的問題是可以1/(3x)+2/(3x)=1/x，也可以x/3+(2x)/3=x，但是我們在電腦上不知道是如何表達的。所以我回答tze ching的問題是1/(3x)+2/(3x)=1/x

1/3x+2/3x = 3/3x = 1/x
點解咁既...
1/3x+2/3x = x(1/3+2/3)=x 囉.....點解係1/x

1. 1/3x+2/3x = 3/3x = 1/x
2. -1/3x-4/3x = -5/3x
3. 2/3x-2-6/2-3x = 2/3x-2-3-3x = 2/3x-5-3x = (2-15x-3x^2)/3x
4. 2/4x+1-6/-4x-1 = 1/2x+x+3/2x = 4/2x+x = 2x+x = 3x
5. 4x/9y-1/3y = (4x-3y)/9y
6. 1/3(r+1)-2/6(1+r) = 1/3(r+1)-1/3(r+1) = 0
7. y/3(4y-9)-3/4(4y-9) = (4y-9)/12(4y-9) = 1/12
8. 3/3a = 1/a
9. 5b^2/10b = b/2
10. 4p/8pq = a/2q
11. -3x^2y/6y^2 = -x^2/2y
12. 2/4x-2y = 1/2x-2y = (1-4xy)/2x
13. y-1/4y-4 = (y-1)/4(y-1) = 1/4
14. 2a/3b*b = 2a/3b^2
15. b/4*6a/ab = b/4 * 6/b = 3/2
16. 7a/5b*b/a^2 = 7/5a