Bài 2 :
b) `5/4 - (7/2 x + 2 1/5) = 0,8`
`⇒ 5/4 - 7/2 x - 11/5 = 4/5`
`⇒ 5/4 - 11/5 - 4/5 = 7/2 x`
`⇒ 7/2 x = -7/4`
`⇒ x = -7/4 : 7/2 = -1/2`
c) `(x + 1/5)(3/4 - 2x) = 0`
$\ ⇒ \left[ \begin{array}{l}x+\dfrac{1}{5}=0\\\dfrac{3}{4} - 2x=0\end{array} \right.$
$\ ⇒ \left[ \begin{array}{l}x=0-\dfrac{1}{5}\\\ 2x=\dfrac{3}{4}\end{array} \right.$
$\ ⇒ \left[ \begin{array}{l}x=\dfrac{-1}{5}\\\ x=\dfrac{3}{8}\end{array} \right.$
d) `(x + 1/5)^2 + 17/25 = 26/25`
`⇒ (x + 1/5)^2 = 26/25 - 17/25`
`⇒ (x + 1/5)^2 = 9/25 = (3/5)^2 = (-3/5)^2`
$\ ⇒ \left[ \begin{array}{l}x+\dfrac{1}{5}=\dfrac{3}{5}\\\ x+\dfrac{1}{5}=\dfrac{-3}{5}\end{array} \right.$
$\ ⇒ \left[ \begin{array}{l}x=\dfrac{3}{5}-\dfrac{1}{5}\\\ x=\dfrac{-3}{5}-\dfrac{1}{5}\end{array} \right.$
$\ ⇒ \left[ \begin{array}{l}x=\dfrac{2}{5}\\\ x=\dfrac{-4}{5}\end{array} \right.$
