\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{98.99.100}\)
\(=\frac{1}{2}\left(\frac{2}{1.2.3}+\frac{2}{2.3.4}+...+\frac{2}{98.99.100}\right)\)
\(=\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{98.99}-\frac{1}{99.100}\right)\)
\(=\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{99.100}\right)\)
\(=\frac{1}{2}.\frac{4949}{9900}\)
\(=\frac{4949}{19800}\)
tính: 1/1.2.3+1/2.3.4+1/3.4.5+...+1/98.99.100
Tính:
B=1/1.2.3+1/2.3.4+1/3.4.5+............+1/98.99.100
Tính A = 1/1.2.3 + 1/2.3.4 + 1/3.4.5 + ............. + 1/ 98.99.100
Tính : a, 1.2.3 + 2.3.4 + 3.4.5 + ... + (n - 1).n.(n+1)
b, 1.2.3 + 3.4.5 + 5.6.7 + 98.99.100
Tính nhanh: D= 1/1.2.3+1/2.3.4 +1/3.4.5+ ..... + 1/98.99.100
1/1.2.3 + 1/2.3.4 + 1/3.4.5+...+1/98.99.100 = ?
1/1.2.3 + 1/2.3.4 + 1/3.4.5 + ...+1/98.99.100 =?
1/1.2.3 +1/2.3.4+1/3.4.5+...+1/98.99.100 = ( 1/k . 1/99.100)
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{98.99.100}\)
Tính
