TA CÓ: \(\frac{1}{n}-\frac{1}{n+5}=\frac{n+5-n}{n\left(n+5\right)}=\frac{5}{n\left(n+5\right)}\)
Thay vào biểu thức trên , ta được:
\(\frac{5}{2.7}+\frac{5}{7.12}+\frac{5}{12.17}+...+\frac{5}{907.1002}=\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+\frac{1}{12}-\frac{1}{17}+...+\frac{1}{907}-\frac{1}{1002}\)
\(=\frac{1}{2}-\frac{1}{1002}=\frac{250}{501}\)
\(\frac{5}{2.7}+\frac{5}{7.12}+\frac{5}{12.17}+\frac{5}{17.22}+\frac{5}{22.29}=?\)
1) Tính nhanh
\(\frac{5}{2.7}+\frac{5}{7.12}+\frac{5}{12.17}+\frac{5}{17.22}+\frac{5}{22.27}+\frac{5}{27.32}+\frac{5}{32.37}\)
Tính tổng:
C=\(\frac{3}{1.5}+\frac{3}{5.9}+\frac{3}{9.13}+...+\frac{3}{101.105}\)
D=\(\frac{4}{2.7}+\frac{4}{7.12}+\frac{4}{12.17}+...+\frac{4}{102.107}\)
E=\(\frac{5}{3.7}+\frac{5}{7.11}+\frac{5}{11.15}+...+\frac{5}{103.107}\)
F=\(\frac{6}{2.7}+\frac{6}{7.12}+\frac{6}{12.17}+...+\frac{6}{102.107}\)
\(\frac{3}{2.7}+\frac{3}{7.12}+\frac{3}{12.17}+...+\frac{3}{2012.2017}\)
\(\frac{3}{2.7}\frac{3}{7.12}\frac{3}{12.17}+....+\frac{3}{2012.2017}\)
Tính : \(N=2015+\frac{10}{2.7}+\frac{10}{7.12}+\frac{10}{12.17}+\frac{10.}{17.22}\)
B=5/2.7+5/7.12+5/12.17+5/17.22+5/22.29
5/2.7 + 5/7.12 + 5/12.17 + 5/17.22 + 5/22.27
/ là phâ`n
tính tổng:
5/2.7 + 5/7.12 + 5/12.17 + 5/22.27
nhanh tay nha mình tick
