Tặng điểm nè Tính a. 3/2.4/9.1/5+2/15 b. (1/2)^2.4/3+8/5:2/5 c. √196- √100 + √9/4 Tìm x, biết a. 2/7x – 1 và 2/5= 3/5 b |x + 5/3| . 9/4 = 19/4 Bài

Bài $1$.

$a$) `3/2 . 4/9 . 1/5 + 2/15`

`= {3.4}/{2.9.5} + 2/15`

`= {2}/{3.5} + 2/15`

`= 2/15 + 2/15`

`= 4/15`.

$b$) `(1/2)^2 . 4/3 + 8/5 : 2/5`

`= 1/4 . 4/3 + 8/5 . 5/2`

`= 1/3 + 8/2`

`= 1/3 + 4`

`= 4 1/3`.

$c$) $\sqrt{196} – \sqrt{100} + \sqrt{\dfrac{9}{4}}$

$= 14 – 10 + \dfrac{3}{4}$

$= 4 + \dfrac{3}{4}$

$= 4\dfrac{3}{4}$.

Bài $2$.

$a$) `2/7 .x – 1 2/5 = 3/5`

`⇔ 2/7 .x – 7/5 = 3/5`

`⇔ 2/7 .x = 10/5 `

`⇔ 2/7 .x = 2`

`⇔ x = 7`  

   Vậy `x=7`.

$b$) `|x+5/3| . 9/4 = 19/4`

`⇔ |x+5/3| = 19/4 . 4/9`

`⇔ |x+5/3| = 19/9`

`⇒` \(\left[ \begin{array}{l}x+\dfrac{5}{3}=\dfrac{19}{9}\\x+\dfrac{5}{3}=-\dfrac{19}{9}\end{array} \right.\) 

$⇒$ \(\left[ \begin{array}{l}x=\dfrac{4}{9}\\x=-\dfrac{34}{9}\end{array} \right.\) 

   Vậy $x$ $∈$ `{4/9;-{34}/9}`.