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\(\frac{2}{3}.\frac{4}{5}+\frac{1}{3}.\frac{4}{5}=\frac{4}{5}\left(\frac{2}{3}+\frac{1}{3}\right)=\frac{4}{5}.\frac{3}{3}=\frac{4}{5}.1=\frac{4}{5}\)
\(\frac{1}{2}:\frac{3}{4}+\frac{1}{6}:\frac{3}{4}=\frac{3}{4}:\left(\frac{1}{2}+\frac{1}{6}\right)=\frac{3}{4}:\frac{2}{3}=\frac{9}{8}\)
\(\frac{2}{3}.\frac{4}{5}-\frac{1}{3}.\frac{4}{5}=\frac{4}{5}\left(\frac{2}{3}-\frac{1}{3}\right)=\frac{4}{5}.\frac{1}{3}=\frac{4}{15}\)
\(\frac{1}{2}:\frac{3}{4}-\frac{1}{6}:\frac{3}{4}=\frac{3}{4}:\left(\frac{1}{2}-\frac{1}{6}\right)=\frac{3}{4}:\frac{1}{3}=\frac{9}{4}\)
\(\frac{2}{3}.\frac{4}{5}+\frac{1}{3}.\frac{4}{5}=\left(\frac{2}{3}+\frac{1}{3}\right).\frac{4}{5}=1.\frac{4}{5}=\frac{4}{5}\)
\(\frac{1}{2}:\frac{3}{4}+\frac{1}{6}:\frac{3}{4}=\frac{1}{2}.\frac{4}{3}+\frac{1}{6}.\frac{4}{3}=\left(\frac{1}{2}+\frac{1}{6}\right).\frac{4}{3}=\frac{2}{3}.\frac{4}{3}=\frac{8}{9}\)
c,d tương tự
\(\left(1-\frac{1}{2}\right)x\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x\left(1-\frac{1}{5}\right)x\left(1-\frac{1}{6}\right)\)
\(=\frac{1}{2}.\frac{2}{3}.\frac{3}{4}.\frac{4}{5}.\frac{5}{6}\)
\(=\frac{1.2.3.4.5}{2.3.4.5.6}=\frac{1}{6}\)
3/5x(2/3-1/5:3/5)
=3/4x(2/3-1/3)
=3/4x1/3=1/4
đúng 100%
\(\frac{3}{4}\cdot\left(\frac{2}{3}-\frac{1}{5}:\frac{3}{5}\right)\)
\(=\frac{3}{4}\cdot\left(\frac{2}{3}-\frac{1}{3}\right)\)
\(=\frac{3}{4}\cdot\frac{1}{3}=\frac{1}{4}\)
\(\frac{3}{4}.8,4+2,8.1\frac{1}{2}\)
\(=\frac{63}{10}+\frac{21}{5}\)
\(=\frac{63}{10}+\frac{42}{10}\)
\(=\frac{63+42}{10}=10,5\)
bài làm
a) \(\frac{5}{8}-\frac{2}{5}\)
\(=\frac{25}{40}-\frac{16}{40}\)
\(=\frac{9}{40}\)
b) \(1\frac{1}{10}-\frac{3}{4}\)
\(=\frac{11}{10}-\frac{3}{4}\)
\(=\frac{22}{20}-\frac{15}{20}\)
\(=\)\(\frac{7}{20}\)
c) \(\frac{2}{3}+\frac{1}{2}-\frac{5}{6}\)
\(=\frac{4}{6}+\frac{3}{6}-\frac{5}{6}\)
\(=\frac{4+3-5}{6}\)
\(=\frac{2}{6}\)
\(=\frac{1}{3}\)
chúc bạn học tốt
\(\left(1-\frac{1}{2}\right)\cdot\left(1-\frac{1}{3}\right)\cdot\left(1-\frac{1}{4}\right)\cdot...\cdot\left(1-\frac{1}{7}\right)\)
\(=\frac{1}{2}\cdot\frac{2}{3}\cdot\frac{3}{4}\cdot\frac{4}{5}\cdot\frac{5}{6}\cdot\frac{6}{7}\)
\(=\frac{\left(1\cdot2\cdot3\cdot4\cdot5\cdot6\right)}{\left(2\cdot3\cdot4\cdot5\cdot6\cdot7\right)}\)
\(=\frac{1}{7}\)
\(M=\frac{1}{1+2}+\frac{1}{1+2+3}+\frac{1}{1+2+3+4}+\frac{1}{1+2+3+4+5}\)
\(M=\frac{1}{\left(1+2\right).2:2}+\frac{1}{\left(1+3\right).3:2}+\frac{1}{\left(1+4\right).4:2}+\frac{1}{\left(1+5\right).5:2}\)
\(M=\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+\frac{2}{5.6}\)
\(M=2.\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\right)\)
\(M=2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\right)\)
\(M=2.\left(\frac{1}{2}-\frac{1}{6}\right)\)
\(M=2.\frac{1}{2}-2.\frac{1}{6}\)
\(M=1-\frac{1}{3}=\frac{2}{3}\)