Question

Tìm x biết :

a) 21 + 3 . x = 39

b) 2x - \(\dfrac{1}{2}\)= \(\dfrac{-9}{10} \): 0,2

Answer 1

a) 21 + 3x = 39

3x = 39 - 21

3x = 18

\(\Rightarrow\) x = 6

Vậy x = 6

b) 2x - \(\dfrac{1}{2}\) = \(\dfrac{-9}{10}\) : 0,2

2x - \(\dfrac{1}{2}\) = \(\dfrac{-9}{10} : \dfrac{2}{10}\)

2x - \(\dfrac{1}{2}\) = \(\dfrac{-9}{2}\)

2x = \(\dfrac{-9}{2} + \dfrac{1}{2}\)

2x = -4

x = -4 : 2

\(\Rightarrow\)x = -2

Vậy x = -2

Answer 2

a) x=6

b)x=-2

Answer 3

a)

\(21+3x=39\\ 3x=39-21\\ 3x=18\\ x=18:3\\ x=6\)

b)

\(2x-\dfrac{1}{2}=\dfrac{-9}{10}:0,2\\ 2x-\dfrac{1}{2}=\dfrac{-9}{10}:\dfrac{1}{5}\\ 2x-\dfrac{1}{2}=\dfrac{-9}{2}\\ 2x=\dfrac{-9}{2}+\dfrac{1}{2}\\ 2x=4\\ x=4:2\\ x=2\)

Answer 4

Nhầm, bạn sửa lại 3 dòng cuối bài b nhé

\(2x=-4\\ x=-4:2\\ x=-2\)