唔知點做方程,help

6x - 9=2x+11,x=?唔該列咪步驟
首先兩邊加 + 9,
6x – 9 + 9 = 2x + 11 +9
6x = 2x + 20
然後兩邊減2x
6x – 2x = 2x + 20 – 2x
4x = 20
x = 20/4 = 5
x = 5

0.4x+0.6x=0.8x=12,x=? 唔該列咪步驟
0.8x = 12
兩邊除0.8
0.8x/0.8 = 12/0.8
x = 15

3/2=q - 7q/8,q=? 唔該列咪步驟
3/2 = q -7q/8
首先兩邊乘8
8 (3/2) =8[q -7q/8]
4(3) = 8q – 7q
12 = q
q = 12

5x/3 - 2x+3/6=7/2 - 2x/3,x=? 唔該列咪步驟
首先兩邊乘6
6(5x/3 - 2x+3/6) = 6(7/2 - 2x/3)

(6)(5x/3) – (6)2x +(6)3/6 = (6)7/2 – (6)2x/3
10x – 12x +3 =21 -4x
– 2x +3 =21 -4x
然後兩邊加4x
– 2x +3 + 4x =21 -4x + 4x
2x +3 = 21
然後兩邊減3
2x +3 - 3 = 21 - 3
2x = 18
x = 18/2
x = 9

Comment:
我教你一方法, 將所有變數 (variable) 放在一邊, 數字放在另外一邊, 改變符號當從一邊走到另外一邊

6x – 9 = 2x+11
6x – 9 -2x = +11 (2x 已經從右邊走到左邊, 改變符號 2x 變-2x)
6x -2x = +11 + 9 (-9 已經從左邊走到右邊, 改變符號 -9 變 +9)
4x = 20
x = 20/4 = 5

5x – 15 + 6 = 2x – 3x +3
5x -2x +3x = 3 +15 – 6 (2x 轉-2x, -3x轉 + 3x)
6x = 12
x = 12/6
x = 2