Câu 10 (1,0 điểm). Tìm x biết: 1. $\frac{5}{2}$x - $\frac{3}{4}$ = $\frac{1}{4}$ 2. $\frac{x + 4}{20}$ = $\frac{5}{x + 4}$

`1)`

     `5/2 x - 3/4 = 1/4`

`⇒ 5/2x = 1/4 + 3/4`

`⇒ 5/2x = 1`

`⇒ x= 1 : 5/2`

`⇒ x= 1 . 2/5`

`⇒ x= 2/5`

Vậy `x= 2/5`

`2)`

     `(x+4)/20 = 5/(x+4)` với `x ne -4`

`⇒ (x+4)(x+4)= 5 . 20`

`⇒ (x+4)^2 = 100`

`⇒ (x+4)^2 = 10^2`

`⇒` \(\left[ \begin{array}{l}x+4=10\\x+4=-10\end{array} \right.\) 

`⇒` \(\left[ \begin{array}{l}x=10-4\\x=(-10) -4\end{array} \right.\) 

`⇒` \(\left[ \begin{array}{l}x=6 (t/m)\\x=-14 (t/m)\end{array} \right.\) 

Vậy `x ∈ {6; -14}`