Bài 3:
a: \(-\dfrac{4}{5}=\dfrac{-4\cdot7}{5\cdot7}=\dfrac{-28}{35}\)
\(\dfrac{6}{7}=\dfrac{6\cdot5}{7\cdot5}=\dfrac{30}{35}\)
b: \(\dfrac{-2}{21}=\dfrac{-2\cdot8}{21\cdot8}=\dfrac{-16}{168}\)
\(\dfrac{-5}{24}=\dfrac{-5\cdot7}{24\cdot7}=\dfrac{-35}{168}\)
c: \(\dfrac{-7}{12}=\dfrac{-7\cdot3}{12\cdot3}=\dfrac{-21}{36}\)
\(\dfrac{11}{-18}=\dfrac{-11}{18}=\dfrac{-11\cdot2}{18\cdot2}=\dfrac{-22}{36}\)
d: \(\dfrac{-15}{45}=\dfrac{-15\cdot4}{45\cdot4}=\dfrac{-60}{180}\)
\(\dfrac{-12}{60}=\dfrac{-12\cdot3}{60\cdot3}=\dfrac{-36}{180}\)
e: \(\dfrac{3}{20}=\dfrac{3\cdot3}{20\cdot3}=\dfrac{9}{60}\)
\(\dfrac{4}{30}=\dfrac{4\cdot2}{30\cdot2}=\dfrac{8}{60}\)
\(\dfrac{7}{15}=\dfrac{7\cdot4}{15\cdot4}=\dfrac{28}{60}\)
f: \(\dfrac{-5}{16}=\dfrac{-5\cdot21}{16\cdot21}=\dfrac{-105}{336}\)
\(\dfrac{11}{24}=\dfrac{11\cdot14}{24\cdot14}=\dfrac{154}{336}\)
\(\dfrac{-21}{56}=\dfrac{-21\cdot6}{56\cdot6}=\dfrac{-126}{336}\)
Bài 2:
a: \(\dfrac{x}{7}=\dfrac{-4}{14}\)
=>\(\dfrac{x}{7}=-\dfrac{2}{7}\)
=>x=-2
b: \(\dfrac{x+3}{2}=\dfrac{-12}{-6}\)
=>\(\dfrac{x+3}{2}=2\)
=>\(x+3=2\cdot2=4\)
=>x=4-3=1
c: \(\dfrac{x}{2}=\dfrac{-2}{-x}\)(ĐKXĐ: x<>0)
=>\(\dfrac{x}{2}=\dfrac{2}{x}\)
=>\(x^2=4\)
=>\(\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)
d: ĐKXĐ: x<>1
\(\dfrac{x-1}{5}=\dfrac{5}{x-1}\)
=>\(\left(x-1\right)\cdot\left(x-1\right)=5^2\)
=>\(\left(x-1\right)^2=25\)
=>\(\left[{}\begin{matrix}x-1=5\\x-1=-5\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=6\left(nhận\right)\\x=-4\left(nhận\right)\end{matrix}\right.\)
e: \(\dfrac{x-1}{3}=\dfrac{8}{6}\)
=>\(\dfrac{x-1}{3}=\dfrac{4}{3}\)
=>x-1=4
=>x=5
f: ĐKXĐ: x<>0
\(\dfrac{x}{9}=\dfrac{4}{x}\)
=>\(x^2=36\)
=>\(\left[{}\begin{matrix}x=6\left(nhận\right)\\x=-6\left(nhận\right)\end{matrix}\right.\)
