\(A=\dfrac{1}{1\times4}+\dfrac{1}{4\times7}+\dfrac{1}{7\times10}+...+\dfrac{1}{100\times103}\)
\(=\dfrac{1}{3}\left(\dfrac{3}{1\times4}+\dfrac{3}{4\times7}+...+\dfrac{3}{100\times103}\right)\)
\(=\dfrac{1}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{100}-\dfrac{1}{103}\right)\)
\(=\dfrac{1}{3}\left(1-\dfrac{1}{103}\right)=\dfrac{1}{3}.\dfrac{102}{103}=\dfrac{34}{103}\)
Tính tổng sau
F= \(\dfrac{1}{1x4}\)+\(\dfrac{1}{4x7}\)+....+\(\dfrac{1}{97x100}\)+\(\dfrac{1}{100x103}\)
11/1x4+11/4x7+11/7x10+...11/100x103
1/5x9+1/9x13+1/13x17+...+1/2450
mình cần gấp nhé
A=\(\dfrac{3}{5x8}\)+\(\dfrac{3}{8x11}\)+\(\dfrac{3}{11x14}\)+....+\(\dfrac{3}{100x103}\)
Cho: S=\(\frac{3}{1x4}+\frac{3}{4x7}+\frac{3}{7x10}+...+\frac{3}{100x103}\). Chứng minh S<1
Tính : 2/1x4+2/4x7+2/7x10+......+2/100x103
Tìm x: (\(\dfrac{1}{2}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{8}\)+\(\dfrac{1}{16}\)) : x= \(\dfrac{1}{2}\)+\(\dfrac{1}{6}\)+...\(\dfrac{1}{132}\)
Tìm y biết: (y- \(\dfrac{1}{2}\)): (\(\dfrac{1}{2}\)+ \(\dfrac{1}{6}\) + \(\dfrac{1}{12}\) + \(\dfrac{1}{20}\)+ ... + \(\dfrac{1}{90}\)) = \(\dfrac{1}{3}\)
Tìm a
a) \(2\dfrac{3}{4}-a+\dfrac{1}{4}=1\dfrac{1}{2}\)
b)3\(\dfrac{1}{4}-a-1\dfrac{3}{4}=\dfrac{7}{8}\)
c) 2\(\dfrac{5}{6}-1\dfrac{1}{2}-a=\dfrac{1}{6}\)
\(\dfrac{1}{1.4}+\dfrac{1}{4.7}+\dfrac{1}{7.10}+\dfrac{1}{10.13}+...+\dfrac{1}{x.\left(x+3\right)}=\dfrac{34}{103}\)
Tìm x
