B = 1/35 + 1/63 + 1/99 + 1/143 + 1/195 + 1/255
= 1/ 5 x 7 + 1 / 7 x 9 + 1 / 9 x 11 + 1 / 11 x 13 + 1 / 13 x 15 + 1 / 15 x 17
= 1/5 - 1/7 + 1/ 7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13 + 1/13 - 1/15 + 1/15 - 1/17
= 1/5 - 1/17
= 17/85 - 5/85
=12/85
\(B=\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}+\frac{1}{195}+\frac{1}{255}\)
\(B=\frac{1}{5x7}+\frac{1}{7x9}+\frac{1}{9x11}+\frac{1}{11x13}+\frac{1}{13x15}+\frac{1}{15x17}\)
\(Bx2=\frac{2}{5x7}+\frac{2}{7x9}+\frac{2}{9x11}+\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}\)
\(Bx2=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}\)
\(Bx2=\frac{1}{5}-\frac{1}{17}=\frac{12}{85}\)
\(B=\frac{12}{85}:2=\frac{6}{85}\)
\(B=\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}+\frac{1}{195}+\frac{1}{225}\)
\(B=\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+\frac{1}{11.13}+\frac{1}{13.15}+\frac{1}{15.17}\)
\(=>2B=\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}\)
\(=>2B=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}\)
\(=>2B=\frac{1}{5}-\frac{1}{17}\)
\(=>2B=\frac{12}{85}\)
\(=>B=\frac{12}{85}:2\)
\(=>B=\frac{6}{85}\)
Chúc bạn học giỏi nha!!!
K cho mik với nhé
\(B=\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+\frac{1}{143}+\frac{1}{195}+\frac{1}{255}\)
\(B=\frac{1}{5x7}+\frac{1}{7x9}+\frac{1}{9x11}+\frac{1}{11x13}+\frac{1}{13x15}+\frac{1}{15x17}\)
\(Bx2=\frac{2}{5x7}+\frac{2}{7x9}+\frac{2}{9x11}+\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}\)
\(Bx2=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}\)
\(Bx2=\frac{1}{5}-\frac{1}{17}=\frac{12}{85}\)
\(B=\frac{12}{85}:2=\frac{6}{85}\)
