11;22;33;44;55;66;77;88;99;110

11 22 33 44 55 66 77 88 99 110 nha e

 11 22 33 44 55 66 77 88 99 100

nhìn tớ

Ta có:

\(\frac{3}{11.16}+\frac{3}{16.21}+\frac{3}{21.26}+...+\frac{3}{61.66}\)

\(=\frac{1}{5}.\left(\frac{1}{11.16}+\frac{1}{16.21}+\frac{1}{21.26}+...+\frac{1}{61.66}\right)\)

\(=\frac{1}{5}.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{61}-\frac{1}{66}\right)\)

\(=\frac{1}{5}.\left(\frac{1}{11}-\frac{1}{66}\right)=\frac{1}{5}.\frac{5}{66}\)

\(=\frac{1}{66}\)

\(\frac{3}{11x16}+\frac{3}{16x21}+\frac{3}{21x26}+.........+\frac{3}{61x66}\)

= \(\frac{3}{11}-\frac{3}{16}+\frac{3}{16}-\frac{3}{21}+\frac{3}{21}-\frac{3}{26}+..........+\frac{3}{61}-\frac{3}{66}\)

=> \(\frac{3}{11}-\frac{3}{66}\)= \(\frac{5}{22}\)

\(\left(\dfrac{6}{11}+\dfrac{5}{11}\right)\times\dfrac{3}{7}=\dfrac{11}{11}\times\dfrac{3}{7}=1\times\dfrac{3}{7}=\dfrac{3}{7}\)

\(\dfrac{3}{5}\left(\dfrac{7}{9}-\dfrac{2}{9}\right)=\dfrac{3}{5}\times\dfrac{5}{9}=\dfrac{1}{3}\)

`( 6 / 11 + 5 / 11 ) xx 3 / 7 = 11 / 11 xx 3 / 7 = 1 xx 3 / 7 = 3 / 7`

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`3 / 5 xx 7 / 9 - 3 / 5 xx 2 / 9 = 3 / 5 xx ( 7 / 9 - 2 / 9 ) = 3 / 5 xx 5 / 9 = 1 / 3`

(6/11+5/11)x3/7

=11/11x3/7

=33/77

3/5x7/9-3/5x2/9

=21/63-6/63

=15/63

\(\frac{5}{1.3}+\frac{5}{3.5}+\frac{5}{5.7}+...+\frac{5}{101.103}\)

\(=\frac{2}{5}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5,7}+...+\frac{2}{101.103}\right)\)

\(=\frac{2}{5}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{101}-\frac{1}{103}\right)\)

\(=\frac{2}{5}\left(1-\frac{1}{103}\right)\)

\(=\frac{2}{5}.\left(\frac{102}{103}\right)=\frac{204}{515}\)

Nhớ kiểm tra lại cho kl nhé

204/515

\(\frac{10}{11}\div\left(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{9\cdot11}\right)\)

\(=\frac{10}{11}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{9}-\frac{1}{11}\right)\)

\(=\frac{10}{11}\left(\frac{1}{3}-\frac{1}{7}+\frac{1}{9}-\frac{1}{11}\right)\)

=> sai đề