Bài 2:
a; \(\frac23+\frac{-4}{7}=\frac{14}{21}-\frac{12}{21}=\frac{14-12}{21}=\frac{2}{21}\)
b: \(-\frac{3}{17}-\left(\frac23-\frac{3}{17}\right)\)
\(=-\frac{3}{17}-\frac23+\frac{3}{17}\)
\(=-\frac23\)
c: \(\frac34-\frac{7}{11}+\left(\frac{18}{11}-\frac34+\frac17\right)\)
\(=\frac34-\frac{7}{11}+\frac{18}{11}-\frac34+\frac17\)
\(=\left(\frac34-\frac34\right)+\left(\frac{18}{11}-\frac{7}{11}\right)+\frac17\)
\(=1+\frac17=\frac87\)
Bài 3:
a: \(\frac{x}{20}=\frac{-3}{4}\)
=>\(x=20\cdot\frac{-3}{4}=-15\)
b: \(-\frac{-6}{12}-x=\frac{9}{48}\)
=>\(\frac12-x=\frac{3}{16}\)
=>\(x=\frac12-\frac{3}{16}=\frac{8}{16}-\frac{3}{16}=\frac{5}{16}\)
c: \(\frac35-\left(2\frac15-x\right)^2=\frac{6}{25}\)
=>\(\frac35-\left(x-\frac{11}{5}\right)^2=\frac{6}{25}\)
=>\(\left(x-\frac{11}{5}\right)^2=\frac35-\frac{6}{25}=\frac{9}{25}\)
=>\(\left[\begin{array}{l}x-\frac{11}{5}=\frac35\\ x-\frac{11}{5}=-\frac35\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac35+\frac{11}{5}=\frac{14}{5}\\ x=-\frac35+\frac{11}{5}=\frac85\end{array}\right.\)
