14) \(0,25x-0,4x=1\)
\(\Rightarrow-0,15x=1\)
\(\Rightarrow x=\dfrac{1}{-0,15}\)
\(\Rightarrow x=-\dfrac{20}{3}\)
15) \(\dfrac{3}{4}x+\dfrac{2}{5}x=1\)
\(\Rightarrow\dfrac{23}{20}x=1\)
\(\Rightarrow x=1:\dfrac{23}{20}\)
\(\Rightarrow x=\dfrac{20}{23}\)
18) \(\dfrac{x-\dfrac{x}{12}+\dfrac{x}{18}}{7-\dfrac{7}{12}+\dfrac{7}{18}}=-\dfrac{12}{21}\)
\(\Rightarrow\dfrac{x-x+x}{7-7+7}=-\dfrac{4}{7}\)
\(\Rightarrow\dfrac{x}{7}=-\dfrac{4}{7}\)
\(\Rightarrow7x=-28\)
\(\Rightarrow x=\dfrac{-28}{7}\)
\(\Rightarrow x=-4\)
13: =>2x+1/2=0 hoặc 2x-3=0
=>x=-1/4 hoặc x=3/2
17: =>x=(x-12)/3
=>3x=x-12
=>2x=-12
=>x=-6
16:=>1/2x-2/3x-2/3=-1/12
=>-1/6x=7/12
=>x=-7/2
