Bài 4:
a) 9-25=(7-x)-(25+7)
⇒ -16=7-x-25-7
⇒ x =7-25-7+16
⇒ x =-9
b) 5x-(3+4x)=5
⇒ 5x-3-4x =5
⇒ x =8
c) -(135+x)+48=x-23
⇒ -135-x+48 =x-23
⇒ -x-x =-23-48+135
⇒ -2x =64
⇒ x =-32
d) |x-1|=4
⇒\(\left[ \begin{array}{l}x-1=4\\x-1=-4\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=5\\x=-3\end{array} \right.\)
Bài 5:
a) $\frac{4}{5}$.${x}$=$\frac{8}{35}$
x =$\frac{8}{35}$:$\frac{4}{5}$
x =$\frac{2}{7}$
b) $\frac{1}{4}$+$\frac{1}{3}$:3x=-5
$\frac{1}{3}$:3x =-5- $\frac{1}{4}$
$\frac{1}{3}$:3x =$\frac{-21}{4}$
3x =$\frac{1}{3}$:$\frac{-21}{4}$
3x =$\frac{-4}{63}$
x =$\frac{-4}{189}$
c) $\frac{2}{3}$x+$\frac{1}{4}$=$\frac{7}{12}$
$\frac{2}{3}$x =$\frac{7}{12}$ -$\frac{1}{4}$
$\frac{2}{3}$x =$\frac{1}{3}$
x =$\frac{1}{2}$
