Tổng quát: \(\frac{1}{n\left(n+1\right)}=\frac{1}{n}-\frac{1}{n+1}\)
\(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+..+\frac{1}{110}=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+....+\frac{1}{10.11}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+....+\frac{1}{10}-\frac{1}{11}\)
\(=\frac{1}{2}-\frac{1}{11}=\frac{9}{22}\)
1/6 + 1/12 + 1/20 + 1/30 + 1/42 +.....+ 1/90 + 1/110
B = 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + ...+ 1/90 + 1/110
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/90+1/110 = ?
Tính:
B = 1/6 + 1/12 + 1/20 + 1/30 + 1/ 42 + .....+1/90 + 1/110
Tính nhanh 1/2 + 1/6 + 1/12+ 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 = .....
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{90}+\frac{1}{110}\)\(\frac{1}{110}\)
\(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+....+\frac{1}{90}+\frac{1}{110}\)= ?
a) 1/2+1/4+1/8+1/16+....+1/512
b) 1/2+1/6+1/12+1/20+1/30+1/42+1/56+...+1/90+1/110
1/6+1/12+1/20+1/30+1/42+.....+1/90+1/110
1/11*16+1/16*21+1/21*26+.....+1/56*61+1/61*66
