Question

giúp bài 5

Answer 1

Câu 5:

\(a)\dfrac{1}{3}+\dfrac{2}{5}+\dfrac{4}{3}+\dfrac{3}{5}+\dfrac{7}{3}.\\ =\left(\dfrac{1}{3}+\dfrac{4}{3}+\dfrac{7}{3}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=\dfrac{12}{3}+\dfrac{5}{5}.\\ =4+1=5.\)

\(b)\dfrac{5}{2}+\dfrac{6}{11}+\dfrac{2}{8}+\dfrac{7}{2}+\dfrac{6}{8}+\dfrac{5}{11}.\\ =\dfrac{5}{2}+\dfrac{6}{11}+\dfrac{1}{4}+\dfrac{7}{2}+\dfrac{3}{4}+\dfrac{5}{11}.\\ =\left(\dfrac{5}{2}+\dfrac{7}{2}\right)+\left(\dfrac{6}{11}+\dfrac{5}{11}\right)+\left(\dfrac{1}{4}+\dfrac{3}{4}\right).\\ =\dfrac{12}{2}+\dfrac{11}{11}+\dfrac{4}{4}.\\ =6+1+1=8.\)

\(c)\dfrac{-1}{8}+\dfrac{6}{7}+\dfrac{2}{14}+\dfrac{-7}{8}+\dfrac{7}{9}.\\ =\dfrac{-1}{8}+\dfrac{6}{7}+\dfrac{1}{7}+\dfrac{-7}{8}+\dfrac{7}{9}.\\ \left(\dfrac{-1}{8}+\dfrac{-7}{8}\right)+\left(\dfrac{6}{7}+\dfrac{1}{7}\right)+\dfrac{7}{9}.\\ =\dfrac{-8}{8}+\dfrac{7}{7}+\dfrac{7}{9}.\\ =\dfrac{7}{9}.\)

\(d)\dfrac{-4}{12}+\dfrac{18}{45}+\dfrac{-6}{9}+\dfrac{-21}{35}+\dfrac{6}{30}.\\ =\dfrac{-1}{3}+\dfrac{2}{5}+\dfrac{-2}{3}+\dfrac{-3}{5}+\dfrac{1}{5}.\\ =\left(\dfrac{-1}{3}+\dfrac{-2}{3}\right)+\left(\dfrac{2}{5}+\dfrac{-3}{5}+\dfrac{1}{5}\right).\\ =\dfrac{-3}{3}+0=-1.\)