中一數學─一元一次方程【20點】

*19)
5[2(x+1)+x]=11x-2
5[2x+2(1)]=11x-2
5(2x)+5(2)=11x-2
10x+10=11x-2
10x-11x=-2-10
-1x=-12
x=-12/-1
x=12

*21)
2c-9/6 -1/2=0
2c-9/6=0+1/2
2c-9/6 (6)=1/2 (6)
2c-9=3
2c=3+9
2c=12
c=12/2
c=6

*23)
a+3/10=2a-1/6
a+3/10 (30)=2a-1/6 (30)
3(a+3)=5(2a-1)
3a+3(3)=5(2a)+5(-1)
3a+9=10a-5
3a-10a=-5-9
-7a=-14
a=-14/-7
a=2

19.
5[2(x+1)+x]=11x-2
5[2x+2+x]=11x-2
10x+10+5x=11x-2
-16x=-12
x=3/4

21.
2c-9/6-1/2=0
2c-9-1/2x3=0
2c-9-1/3=0
2c=0+9+1/3
2c=28/3
c=28/3x1/2
c-14/3

23.
a+3/10=2a-1/6
30xa+3/10=2a-1/6x30
3a+9=10a-5
3a-10a=-9-5
a=-14/-7
a=2

ps:第21同23題個x即係乘
希望幫到你._.''有唔明可以搵我xd

19.

5【2(x+1)+x】+x = 11x -2
5(2x+2+x) = 11x -2
5(3x+2) = 11x -2
15x+10 = 11x -2
15x-11x = -2-10
4x = -12
x = -3

21. (2c-9)/6- 1/2 = 0
(2c-9)/6 = 1/2
2c-9= 1/2 *6
2c-9= 3
2c = 3+9
2c = 12
c = 6

23. (a+3)/10 = (2a-1)/6
(a+3) *6 = (2a-1) *10
6a+18 = 20a-10
18+10 = 20a-6a
8 = 14a
a = 14/8
a = 7/4

2009-11-30 18:31:01 補充：
修正：

23. (a+3)/10 = (2a-1)/6
(a+3) *6 = (2a-1) *10
6a+18 = 20a-10
18+10 = 20a-6a
28 = 14a
a = 28/14
a = 2

5(2(X+1)+X)=11X-2

5(2X+2+X)=11X-2

10X+10+5X=11X-2

15X-11X=-2-10

4X=-12

X=-3



(2C-9)/6-1/2=0

2C-9-6(1/2)=0

2C=9+3

C=6



(A+3)/10=(2A-1)/6

6(A+3)=10(2A-1)

6A+18=20A-10

14A=28

A=2

2009-12-02 14:01:39 補充：
ON99我ce maths拎a(文科)19題點會12 kai上腦