Question

Tìm x:

a) (x-2) (5 x +15) = 0

 

b) 5 x - 3 = -18

 

c) 3/7 + x = 0

 

d) 3 x - (-1/4) = 0,4

 

 

Answer 1

a) (x-2) (5 x +15) = 0

→  (x-2) =0 hoặc (5 x +15) = 0 ​

TH1:x-2=0→x=0+2→x=2

TH2:5x+15=0→5x=0-15→5x=-15→x=-15/5→x=-3

vậy x=2 hoặc x=-3

b) 5 x - 3 = -18

5x=-18+3

5x=-15

x=-15:5

x=-3

 c) 3/7 + x = 0

x=0-3/7

x=-3/7

 d) 3 x - (-1/4) = 0,4

⇔3x+1/4=2/5

3x=2/5-1/4

3x=3/20

→x=3/20:3

→x=1/20

 

Answer 2

 `(x-2) (5 x +15) = 0`

\(=>\left[{}\begin{matrix}x-2=0\\5x+15=0\end{matrix}\right.=>\left[{}\begin{matrix}x=2\\5x=-15\end{matrix}\right.=>\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\)

___________________________________________

` 5 x - 3 = -18`

`5x = -15`

` x = -15 :5`

` x = -3`

______________________________________

`3/7 + x = 0`

` x = 0 - 3/7`

`x = -3/7`

______________________________

`3 x - (-1/4) = 0,4`

`3x + 1/4 = 0,4`

` 3x= 0,4 - 1/4`

`3x=3/20`

` x = 3/20 : 3`

` x = 1/20`