=(5/5-5/10+5/10-5/15+.........+5/2015-5/2020)
=(1/5-1/10+1/10-1/20+.......+1/2015-1/2020)
=1/5-1/2020
=403/2020
ai tích mk mk vs
\(\frac{5}{5.10}+\frac{5}{10.15}+.............+\frac{5}{2015.2020}\)
\(=\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+..............+\frac{1}{2015}-\frac{1}{2020}\)
\(=\frac{1}{5}-\frac{1}{2020}\)
\(=\frac{403}{2020}\)
5/5.10+5/10.15+5/15.20+...+5/2015.2020
=5(1/5.10+1/10.15+1/15.20+...+1/2015.2020) khoang cach tu 5-10;10-15;...;2015-2020 la 5 suy ra
=5/5(1/5-1/10+1/10-1/15+1/15-1/20+...+1/2015-1/2020) ; (-1/5+1/5;-1/10+1/10;-1/15+1/15;-1/20+1/20;... bang 0)
=1(1/5-1/2020)=2015/10100=403/2020
