4/15 + 4/35 + 4/63 + 4/99 + 4/143 = 20/39

A = 4/5.7 + 4/7.9 +... +4/15.17

=> 1/2.A = 2/5.7 + 2/7.9 +...+ 2/15.17

= 1/5 - 1/7 + 1/7 - 1/9 +...+1/15 - 1/17

= 1/5 - 1/17

= 17/85 - 5/85

=12/85

=> A = 12/85 : 1/2 = 12/85 . 2 = 24/85

 ​​4/15+ 4/35+ 4/63+ 4/99=16/33

​chúc bạn hok tốt

\(\frac{4}{12}+\frac{4}{35}+\frac{4}{63}+\frac{4}{99}\)

\(=2.\left(\frac{2}{12}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}\right)\)

\(=2.\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right)\)

\(=2.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)

\(=2.\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=2.\left(\frac{11}{33}-\frac{3}{33}\right)\)

\(=2.\frac{8}{33}\)

\(=\frac{16}{33}\)

Tham khảo nhé~

\(\frac{4}{15}+\frac{4}{35}+\frac{4}{63}+\frac{4}{99}\)

\(=4\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=4\left(\frac{2}{21}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=4\left(\frac{1}{9}+\frac{1}{99}\right)\)

\(=4\cdot\frac{4}{33}=\frac{16}{33}\)

a) ta có : A= 149.151 = 149.(150 + 1) = 149 . 150 + 149

   lại có : B= 150.150 = 150.(149+1) = 150.149 + 150

Vì 149<150 => 149.150+149 < 150.149 + 150

=> A<B.Vậy A<B

b) ta có : C= 36.63 - 57 = (35+1).63-57 = 63.35 + 63 - 57= 63.35 + 6

Vì 6<36 => 63.35 + 6 < 36 + 63.35

=> C <D

vậy C<D

Chúc bn học giỏi nhe

a, A=149.151=22499

    B=150.150=22500

b, C=36.63-57=2211

    D=36+63.35=2241

a) A=149(150+1)=149.150+149

    B=(149+1)150=149.150+150

=>B>A

b)C=(35+1)63-57=35.63+6<35.63+36=D

=>D>C

=>

\(\frac{6}{35}+\frac{6}{63}+\frac{6}{99}+...+\frac{6}{255}\)

\(=3\left(\frac{2}{35}+\frac{2}{63}+\frac{2}{99}+...+\frac{2}{255}\right)\)

\(=3\left(\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot11}+...+\frac{2}{15\cdot17}\right)\)

\(=3\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{15}-\frac{1}{17}\right)\)

\(=3\left(\frac{1}{5}-\frac{1}{17}\right)\)

\(=3\cdot\frac{12}{85}=\frac{36}{85}\)

thanks

4/15 + 4/35 + 4/63 + 4/99 + 4/143

= 8/21 + 8/77 + 4/143

= 16/33 + 4/143

= 20/39

\(\frac{4}{15}+\frac{4}{35}+\frac{4}{63}+\frac{4}{99}+\frac{4}{143}\)

\(=2\times\left(\frac{1}{3\times5}+\frac{1}{5\times7}+...+\frac{1}{11\times13}\right)\)

\(=2\times\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{13}\right)\)

\(=2\times\left(\frac{1}{3}-\frac{1}{13}\right)\)

\(=2\times\frac{10}{39}\)

\(=\frac{20}{39}\)