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25 tháng 8

A =   1\(\dfrac{1}{3}\) x 1\(\dfrac{1}{8}\) x 1\(\dfrac{1}{15}\) x 1\(\dfrac{1}{24}\) x ... x 1\(\dfrac{1}{99}\)

A =   \(\dfrac{4}{3}\) x \(\dfrac{9}{8}\) x \(\dfrac{16}{15}\) x \(\dfrac{25}{24}\) x ... x \(\dfrac{100}{99}\)

A =   \(\dfrac{2\times2}{1\times3}\) x \(\dfrac{3\times3}{2\times4}\) x \(\dfrac{4\times4}{3\times5}\) x \(\dfrac{5\times5}{4\times6}\) x ... x \(\dfrac{10\times10}{9\times11}\)

A =    \(\dfrac{\left(2\times3\times...\times9\times10\right)\times\left(2\times3\times4\times...\times10\right)}{\left(1\times2\times3\times..\times9\right)\times\left(3\times4\times..\times10\times11\right)}\)

A =    (\(\dfrac{2\times3\times..\times9}{2\times3\times..\times9}\times\dfrac{10}{1}\)) x (\(\dfrac{3\times4\times...\times9\times10}{3\times4\times...\times9\times10}\) \(\times\)\(\dfrac{2}{11}\) )

A =    \(\dfrac{10}{1}\) \(\times\) \(\dfrac{2}{11}\) 

A =    \(\dfrac{20}{11}\)

 

\(1\dfrac{1}{3}\cdot1\dfrac{1}{8}\cdot...\cdot1\dfrac{1}{99}\)

\(=\dfrac{4}{3}\cdot\dfrac{9}{8}\cdot...\cdot\dfrac{100}{99}\)

\(=\dfrac{2\cdot3\cdot...\cdot10}{1\cdot2\cdot...\cdot9}\cdot\dfrac{2\cdot3\cdot...\cdot10}{3\cdot4\cdot...\cdot11}\)

\(=\dfrac{10}{1}\cdot\dfrac{2}{11}=\dfrac{20}{11}\)

3 tháng 7 2019

a 168 x 168 - 168 x 58/110

= 168 x (168 - 58/100)

= 168 x 8371/50

= 28126,56

b 1/20 + 1/30 + 1/42 + ... + 1/156

= 1/(4x5) + 1/(5x6) + 1/(6x7) + ... + 1/(12x13)

= 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + ... + 1/12 - 1/13

= 1/4 - 1/13

= 9/52

22 tháng 2 2017

\(1\frac{1}{3}.1\frac{1}{8}.1\frac{1}{15}.....1\frac{1}{99}\)

\(=\frac{4}{3}.\frac{9}{8}.\frac{16}{15}......\frac{100}{99}\)

\(=\frac{2.2}{1.3}.\frac{3.3}{2.4}.\frac{4.4}{3.5}.....\frac{10.10}{9.11}\)

\(=\frac{\left(2.3.4...10\right)\left(2.3.4....10\right)}{\left(1.2.3...9\right)\left(3.4.5....11\right)}\)

\(=\frac{10.2}{11}=\frac{20}{11}\)

23 tháng 6 2015

B=3/2x4/3x...........x2018/2017

=3x4x5x...........x2018/2x3x2x2x............x2017

=2x2018

=4036

A,C tương tự

\(=\dfrac{4}{3}\cdot\dfrac{9}{8}\cdot\dfrac{16}{15}\cdot\dfrac{25}{24}\cdot\dfrac{36}{35}=\dfrac{12}{7}\)

9 tháng 12 2022

= 4/3*9/8*16/15*25/24*36/35

=2*2/1*3 * 3*3/2*4 *4*4/3*5 *5*5/4*6 * 6*6/5*7

= (2*3*4*5*6 / 1*2*3*4*5) * ( 2*3*4*5*6 / 3*4*5*6*7)

=6/1* 2/7 

= 12/7

 

11 tháng 8 2016

\(=\frac{4}{3}.\frac{9}{8}.\frac{16}{15}.\frac{25}{24}...\frac{100}{99}\)

11 tháng 8 2016

\(1\frac{1}{3}\times1\frac{1}{8}\times1\frac{1}{15}\times1\frac{1}{24}\times...\times1\frac{1}{99}\)

\(=\frac{4}{3}\times\frac{9}{8}\times\frac{16}{15}\times\frac{25}{24}\times...\times\frac{100}{99}\)

\(=\frac{2\times2}{1\times3}\times\frac{3\times3}{2\times4}\times\frac{4\times4}{3\times5}\times\frac{5\times5}{4\times6}\times...\times\frac{10\times10}{9\times11}\)

\(=\frac{2}{1}\times\frac{10}{11}\)

\(=\frac{20}{11}\)