a: \(\dfrac{2}{3}-\dfrac{1}{2}x=\dfrac{3}{4}\)
=>\(\dfrac{1}{2}x=\dfrac{2}{3}-\dfrac{3}{4}=\dfrac{8-9}{12}=\dfrac{-1}{12}\)
=>\(x=-\dfrac{1}{12}:\dfrac{1}{2}=-\dfrac{1}{12}\cdot2=-\dfrac{1}{6}\)
b: \(-\dfrac{x}{3}=2\dfrac{1}{7}:\dfrac{5}{7}\)
=>\(\dfrac{x}{-3}=\dfrac{15}{7}:\dfrac{5}{7}=\dfrac{15}{7}\cdot\dfrac{7}{5}=3\)
=>\(x=-3\cdot3=-9\)
c: \(\dfrac{5}{4}+\dfrac{1}{4}:x=1\dfrac{3}{8}\)
=>\(\dfrac{1}{4}:x=\dfrac{11}{8}-\dfrac{5}{4}=\dfrac{11}{8}-\dfrac{10}{8}=\dfrac{1}{8}\)
=>\(x=\dfrac{1}{4}:\dfrac{1}{8}=\dfrac{1}{4}\cdot8=2\)
d: \(\left(3,5-2x\right)\cdot1\dfrac{1}{3}=-20\%\)
=>\(\left(3,5-2x\right)\cdot\dfrac{4}{3}=-\dfrac{1}{5}\)
=>\(3,5-2x=-\dfrac{1}{5}:\dfrac{4}{3}=-\dfrac{1}{5}\cdot\dfrac{3}{4}=-\dfrac{3}{20}\)
=>\(2x=\dfrac{7}{2}+\dfrac{3}{20}=\dfrac{73}{20}\)
=>\(x=\dfrac{73}{20}:2=\dfrac{73}{40}\)
e: \(\dfrac{5^x}{125}=5\)
=>\(5^x=5\cdot125=625\)
=>\(5^x=5^4\)
=>x=4
