\(C=70.\left(131313.\left(\dfrac{1}{565656}+\dfrac{1}{727272}+\dfrac{1}{909090}\right)\right)\)

\(C=70.\left(131313.\dfrac{1}{235690}\right)\)

\(C=70.\dfrac{39}{70}\)

\(C=39\)

b: Ta có: \(B=\dfrac{1}{4\cdot9}+\dfrac{1}{9\cdot14}+...+\dfrac{1}{64\cdot69}\)

\(=\dfrac{1}{5}\left(\dfrac{5}{4\cdot9}+\dfrac{5}{9\cdot14}+...+\dfrac{5}{64\cdot69}\right)\)

\(=\dfrac{1}{5}\left(\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{14}+...+\dfrac{1}{64}-\dfrac{1}{69}\right)\)

\(=\dfrac{1}{5}\cdot\dfrac{65}{4\cdot69}\)

\(=\dfrac{13}{276}\)

\(A=\dfrac{2}{1\cdot4}+\dfrac{2}{4\cdot7}+...+\dfrac{2}{97\cdot100}\\ A=\dfrac{2}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{97\cdot100}\right)\\ A=\dfrac{2}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\\ A=\dfrac{2}{3}\left(1-\dfrac{1}{100}\right)=\dfrac{2}{3}\cdot\dfrac{99}{100}=\dfrac{33}{50}\\ B=\dfrac{1}{4\cdot9}+\dfrac{1}{9\cdot14}+...+\dfrac{1}{64\cdot69}\\ B=\dfrac{1}{5}\left(\dfrac{5}{4\cdot9}+\dfrac{5}{9\cdot14}+...+\dfrac{5}{64\cdot69}\right)\\ B=\dfrac{1}{5}\left(\dfrac{1}{4}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{14}+...+\dfrac{1}{64}-\dfrac{1}{69}\right)\\ B=\dfrac{1}{5}\left(\dfrac{1}{4}-\dfrac{1}{69}\right)=\dfrac{1}{5}\cdot\dfrac{65}{276}=\dfrac{13}{276}\)

\(C=70\left(\dfrac{13}{56}+\dfrac{13}{72}+\dfrac{13}{90}\right)=70\cdot13\left(\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}\right)\\ C=910\left(\dfrac{1}{7\cdot8}+\dfrac{1}{8\cdot9}+\dfrac{1}{9\cdot10}\right)\\ C=910\left(\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\right)\\ C=910\left(\dfrac{1}{7}-\dfrac{1}{10}\right)=910\cdot\dfrac{3}{70}=39\)

\(B=70.\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

\(B=70.\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

\(B=70.13.\left(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)

\(B=910.\left(\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)

\(B=910.\left(\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

\(B=910.\left[\frac{1}{7}+\left(\frac{1}{8}-\frac{1}{8}\right)+\left(\frac{1}{9}-\frac{1}{9}\right)-\frac{1}{10}\right]\)

\(B=910.\left[\frac{1}{7}-\frac{1}{10}\right]\)

\(B=910.\frac{3}{70}=39\)

~ Hok tốt ~

#)Giải :

\(B=70.\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

\(B=70.\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)( cùng chia cho 10101 )

\(B=70.\frac{39}{70}\)

\(B=39\)( trên dưới tử mẫu có 70 => loại )

        #~Will~be~Pens~#

39 nha bn

70.(13/56+13/72+13/90)

=70.39/70=39

đúg nha

B=39 tick cho mình nha nha nha nha

\(B=70\cdot\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

\(B=70\cdot\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

\(B=70\cdot\frac{39}{70}\)

\(B=39\)

Vậy B = 39

B=\(70\times\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

B=\(70\times\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

B=\(70\times\frac{39}{70}\)

B=\(39\)

Nếu mk làm sai thì xin lỗi bạn nhiều nha

B=70.\(\left(\frac{13.10101}{56.10101}+\frac{13.10101}{72.10101}+\frac{13.10101}{90.10101}\right)\)

B=70.\(\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

B=70.\(\frac{39}{70}\)=39

ks nha

B= 70.( 131313/565656 + 131313/727272 + 131313/909090)

B = 70 * ( 13/56 + 13/72 + 13/90)

B = 70* 0,1464....

B= 10,254050...

olm.vn/hoi-dap/question/520458.html

\(B=70\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

\(B=70\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

\(B=70.13\left(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)

\(B=70.13.\frac{3}{70}\)

\(B=39\)

\(B=70\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

   \(=70\left(\frac{13.10101}{56.10101}+\frac{13.10101}{72.10101}+\frac{13.10101}{90.10101}\right)\)

   \(=70\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

   \(=70.13\left(\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)

   \(=910\left(\frac{45}{2520}+\frac{35}{2520}+\frac{28}{2520}\right)\)

   \(=910.\frac{3}{70}\)

   \(=39\)

Vậy \(B=39\)

C=39 nha 

70x(13/56+13/72+13/90)

\(70\cdot\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

\(=70\cdot\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

\(=70\cdot\frac{39}{70}\)

\(=70\)

\(70\cdot\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)

\(=70\cdot\left(\frac{13}{56}+\frac{13}{72}+\frac{13}{90}\right)\)

\(=70\cdot\frac{39}{70}\)

\(=39\)

\(\Leftrightarrow\dfrac{2}{3x}-\dfrac{780}{11}:\left[13\left(\dfrac{1}{15}+\dfrac{1}{35}+\dfrac{1}{63}+\dfrac{1}{99}\right)\right]=-5\)

\(\Leftrightarrow\dfrac{2}{3x}-\dfrac{780}{11}:\left[\dfrac{13}{2}\left(\dfrac{2}{15}+\dfrac{2}{35}+\dfrac{2}{63}+\dfrac{2}{99}\right)\right]=-5\)

\(\Leftrightarrow\dfrac{2}{3x}-\dfrac{780}{11}:\left[\dfrac{13}{2}\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\right)\right]=-5\)

\(\Leftrightarrow\dfrac{2}{3x}-\dfrac{780}{11}:\left[\dfrac{13}{2}\cdot\dfrac{8}{33}\right]=-5\)

\(\Leftrightarrow\dfrac{2}{3x}-45=-5\)

=>2/3x=40

=>3x=1/20

hay x=1/60