中一數學 (4)

0.4-0.6(x-3)=1/3(x)-3/5(x-7)

-0.2(x-3)=1/3(x)-3/5(x-7)
把小數點轉換成分數

-1/5(x-3)=1/3(x)-3/5(x-7)
然後要通分母, 所以要乘15

-1/5*15(x-3)=1/3*15(x)-3/5*15(x-7)
-3(x-3)=5(x)-9(x-7)
-3x+9=5x-9x+63
-3x+4x=63-9
x=54

This is an equation contaring x as variable( sorry I don't type Chinese, hope you don't mind)

you should first note that 0.4=2/5
0.6=3/5

so the equation can be now written as:

0.4-0.6(x-3)=1/3(x)-3/5(x-7)
2/5 -3/5(x-3)=1/3(x)-3/5(x-7)
multiply both sides by 15,
6-9(x-3)=5x-9(x-7)
6-9x+27=5x-9x+63
rearranging,
33-9x=-4x+63
-30=5x
x=-6

check:
LHS= 2/5-3/5(-6-3) (sub x=6 into into LHS of the equation)
= 29/5
RHS:
=1/3(-6)-3/5(-6-7)
=-2-3/5(-13)
=29/5
LHS=RHS
so we can claim that x=-6 is the solution to the equation

hope you cna understand my poor presetation

先通分母,

3,5的LCM 是15

15[0.4-0.6(x-3)]=15[1/3(x)-3/5(x-7)]
15(0.4) - 15(0.6)(x-3) = 5x - 9(x-7)


兩邊 x 10 使所有數都變得容易處理

10[15(0.4) - 15(0.6)(x-3)] = 10[5x - 9(x-7)]
15(4) - 15(6)(x-3) = 50x - 90(x-7)
60 - 90(x-3) = 50x - 90x +630
60 - 90x + 270 = -40x +630
-50x = 630-270-60
-50x = 300
x= -6

答案是 -6