方程 + 有向數 問題

下次算式寫成這樣就不會走位:

1. 3+(2x/5) = 21
(2x/5)=18
2x=90
x=45

2. 0.4y+4.7= 12.4
0.4y=7.7
y=19.25


3. 2 [x+(3/10)] = 13.8
2x+(6/10)= 13.8
2x=13.2
x=6.6

4. 10 = 2.9x -8/5
11.6 = 2.9x
4=x
x=4

5. 4 (y --1) --1 =4
4y-4-1=4
4y-5=4
4y=9
y=2.25

6. 2 (2x +3 ) --7 =0
4x+6-7=0
4x-1=0
4x=1
x=0.25

7. (3y-5)/7 - (1/2)= 1/14
(3y-5)/7 = 4/7
(3y-5)= 4
3y=9
y=3


8. ( -14.6) + ( +3.7)
= -10.9

9. [- 8 (4/5) ] / [ - 1 (1/10) ]
= [- 8 (4/5) ] / [ - 1 (1/10) ]
= -6.4/-10
=0.64

10. [ (+6 ) -- (-4) x (+2) ] / ( -2)
=[ (+6 ) - (-4) x (+2) ] / ( -2)
=[ (+6 ) - (-8) ] / ( -2)
=14/-2
= -7