= 13/15 + 13/35 + 13/63 + 13/99
= 13/ 3×5 + 13/5×7 + 13/7×9 + 13/9×11
= 13 x 1/2( 1/3 – 1/5 + 1/5 – 1/7 +1/7 – 1/9 +1/9 – 1/11)
= 13/2 x ( 1/3 – 1/11)
= 13/2 x 8/33 = 104/66=52/33

\(D=\frac{13}{15}+\frac{13}{35}+\frac{13}{63}+\frac{13}{99}\)

\(D=\frac{13}{3}\times5+\frac{13}{5}\times7+\frac{13}{7}\times9+\frac{13}{9}\times11\)

\(D=13\times\frac{1}{2}\left(\frac{1}{3}-\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)

\(D=\frac{13}{2}\times\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(D=\frac{13}{2}\times\frac{8}{33}=\frac{104}{66}=\frac{52}{33}\)

\(D=\frac{52}{33}\)

(131313/151515+ 131313/353535+131313/636363+131313/999999)*33

=(13/15+13/35+13/63+13/99)*33

=52/33*33

=52

131313/151515+131313/353535+131313/636363+131313/999999=13/15+13/35+13/63+13/99

=52/33=1/19/33

​DUYỆT NHÉ

thuy hang beautyful lam chuan

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left(\dfrac{131313}{151515}+\dfrac{131313}{353535}+\dfrac{131313}{636363}+\dfrac{131313}{999999}\right)=-5\)

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left(\dfrac{13}{15}+\dfrac{13}{35}+\dfrac{13}{63}+\dfrac{13}{99}\right)=-5\)

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left(\dfrac{13}{3.5}+\dfrac{13}{5.7}+\dfrac{13}{7.9}+\dfrac{13}{9.11}\right)=-5\)

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left[\dfrac{13}{2}.\left(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}\right)\right]=-5\)

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left[\dfrac{13}{2}.\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\right)\right]=-5\)

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left[\dfrac{13}{2}.\left(\dfrac{1}{3}-\dfrac{1}{11}\right)\right]=-5\)

\(\dfrac{2}{3}x-70.\dfrac{10}{11}:\left[\dfrac{13}{2}.\dfrac{8}{33}\right]=-5\)

\(\dfrac{2}{3}x-\dfrac{700}{11}:\dfrac{52}{33}=-5\)

\(\dfrac{2}{3}x-\dfrac{525}{13}=-5\)

\(\dfrac{2}{3}x=-5+\dfrac{525}{13}=\dfrac{460}{13}\)

\(x\) = \(\dfrac{460}{13}:\dfrac{2}{3}=\dfrac{690}{13}\).

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

\(\Leftrightarrow\frac{2}{3}x-40=0\)

\(\Leftrightarrow x=60\)