Bài 8:
\(A=\dfrac{25}{3}-\dfrac{46}{5}-\dfrac{18}{7}+\dfrac{5}{3}+\dfrac{126}{5}-\dfrac{37}{2}\)
\(A=\left(\dfrac{25}{3}+\dfrac{5}{3}\right)+\left(-\dfrac{46}{5}+\dfrac{126}{5}\right)-\left(\dfrac{18}{7}+\dfrac{37}{2}\right)\)
\(A=\dfrac{30}{3}+\dfrac{80}{5}-\left(\dfrac{36}{14}+\dfrac{259}{14}\right)\)
\(A=10+16+\dfrac{295}{14}\)
\(A=\dfrac{140}{14}+\dfrac{224}{14}-\dfrac{295}{14}\)
\(A=\dfrac{69}{14}\)
Bài 9:
\(a,\dfrac{1}{12}-\left(-\dfrac{1}{6}-\dfrac{1}{4}\right)\)
\(=\dfrac{1}{12}-\left(\dfrac{-2}{12}-\dfrac{3}{12}\right)\)
\(=\dfrac{1}{12}-\dfrac{-5}{12}\)
\(=\dfrac{6}{12}=\dfrac{1}{2}\)
\(b,\dfrac{1}{3}-\left[\left(-\dfrac{5}{4}\right)-\left(\dfrac{1}{4}+\dfrac{3}{8}\right)\right]\)
\(=\dfrac{1}{3}-\left[\dfrac{-5}{4}-\left(\dfrac{2}{8}+\dfrac{3}{8}\right)\right]\)
\(=\dfrac{1}{3}-\left[\dfrac{-5}{4}-\dfrac{5}{8}\right]\)
\(=\dfrac{1}{3}-\left[\dfrac{-10}{8}-\dfrac{5}{8}\right]\)
\(=\dfrac{1}{3}-\dfrac{-15}{8}\)
\(=\dfrac{8}{24}+\dfrac{45}{24}\)
\(=\dfrac{53}{24}\)
\(c,\dfrac{3}{4}-\left[\left(-\dfrac{5}{3}\right)+\left(\dfrac{1}{12}-\dfrac{2}{9}\right)\right]\)
\(=\dfrac{3}{4}-\left[\dfrac{-5}{3}+\dfrac{1}{12}-\dfrac{2}{9}\right]\)
\(=\dfrac{3}{4}+\dfrac{5}{3}-\dfrac{1}{12}+\dfrac{2}{9}\)
\(=\left(\dfrac{3}{4}-\dfrac{1}{12}\right)+\left(\dfrac{5}{3}+\dfrac{2}{9}\right)\)
\(=\left(\dfrac{9}{12}-\dfrac{1}{12}\right)+\left(\dfrac{15}{9}+\dfrac{2}{9}\right)\)
\(=\dfrac{8}{12}+\dfrac{17}{9}\)
\(=\dfrac{2}{3}+\dfrac{17}{9}\)
\(=\dfrac{6}{9}+\dfrac{17}{9}\)
\(=\dfrac{23}{9}\)
