Trường Học

Trường Học

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Ta làm như sau:

   \(\frac{6}{18}\)+\(\frac{6}{54}\)+\(\frac{6}{108}\)+...+\(\frac{6}{990}\)

=\(\frac{6}{3.6}\)+\(\frac{6}{6.9}\)+\(\frac{6}{9.12}\)+...\(\frac{6}{30.33}\)

=2 (\(\frac{3}{3.6}\)+\(\frac{3}{6.9}\)+\(\frac{3}{9.12}\)+...+\(\frac{3}{30.33}\)

=2 (\(\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{9}+\frac{1}{9}-\frac{1}{12}+...+\frac{1}{30}-\frac{1}{33}\))

=2 ( \(\frac{1}{3}-\frac{1}{33}\))

=2.\(\frac{10}{33}\)=\(\frac{2.10}{33}\)=\(\frac{20}{33}\)