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\(A=\frac{1}{1\times2\times3}+\frac{1}{2\times3\times4}+\frac{1}{3\times4\times5}+...+\frac{1}{36\times37\times38}+\frac{1}{37\times38\times39}\)
\(2A=\frac{2}{1\times2\times3}+\frac{2}{2\times3\times4}+\frac{2}{3\times4\times5}+...+\frac{2}{36\times37\times38}+\frac{2}{37\times38\times39}\)
\(2A=\frac{1}{1\times2}-\frac{1}{2\times3}+\frac{1}{2\times3}-\frac{1}{3\times4}+...+\frac{1}{37\times38}-\frac{1}{38\times39}\)
\(2A=\frac{1}{1\times2}-\frac{1}{38\times39}\)
\(2A=\frac{741}{1482}-\frac{1}{1482}\)
\(2A=\frac{370}{741}\)
\(A=\frac{370}{741}:2=\frac{185}{741}\)
\(\frac{2}{3}+\frac{5}{8}+\frac{9}{3}:\frac{4}{7}.\left(\frac{2}{6}+\frac{1}{1}\right)\)
\(=\frac{2}{3}+\frac{5}{8}+3:\frac{4}{7}.\left(\frac{1}{3}+1\right)\)
\(=\frac{2}{3}+\frac{5}{8}+\frac{21}{4}.\frac{4}{3}\)
\(=\frac{2}{3}+\frac{5}{8}+7\)
\(=\frac{16}{24}+\frac{15}{24}+7\)
\(=\frac{31}{24}+7\)
\(=\frac{19}{12}\)
Mình không biết đúng hay sai, nhưng mà kết bạn nha!
26/27-5/3=-19/27
43770:126=347(dư 48)
=31/10 :10/3=93/100
Hok tốt nha ban!!!
\(=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}\)
\(=\frac{10}{30}+\frac{5}{30}+\frac{3}{30}+\frac{2}{30}\)
\(=\frac{20}{30}=\frac{2}{3}\)
a) \(\frac{3}{5}\times\frac{8}{27}\times\frac{5}{3}\)
\(=\left(\frac{3}{5}\times\frac{5}{3}\right)\times\frac{8}{27}\)
\(=1\times\frac{8}{27}\)
\(=\frac{8}{27}\)
b) \(\frac{7}{19}\times\frac{1}{3}+\frac{7}{19}\times\frac{2}{3}\)
\(=\frac{7}{19}\times\left(\frac{1}{3}+\frac{2}{3}\right)\)
\(=\frac{7}{19}\times1\)
\(=\frac{7}{19}\)
Ta có: \(\frac{2}{2.3.4}+\frac{2}{3.4.5}+...+\frac{2}{37.38.39}\)
\(\Rightarrow\frac{1}{2.3}-\frac{1}{3.4}+\frac{1}{3.4}-\frac{1}{4.5}+.....+\frac{1}{37}-\frac{1}{38}+\frac{1}{38}-\frac{1}{39}\)
\(=\frac{1}{2.3}-\frac{1}{38.39}=\frac{41}{247}\)