\(=\frac{20}{112}+\frac{20}{280}+\frac{20}{520}+...+\frac{20}{2800}=20\left(\frac{1}{8.14}+\frac{1}{14.20}+\frac{1}{20.26}+...+\frac{1}{50.56}\right)\)
\(=20\left(\frac{1}{8}-\frac{1}{56}\right)=20.\frac{3}{28}=\frac{15}{7}\)
H = 10/56+10/140+10/260+10/1400
10/56+10/140+10/260+.....+10/1400
Tính tổng:A=10/56+10/140+10/260+.........+10/1400
A=-10/56+-10/140+-10/260+...+-10/1400
10/56 + 10/140 + 10/260 + ...+ 10/1400
tính: 10/56+10/140+10/260+...+10/1400
A=10/56+10/140+10/260+......+10/1400
tính tổng M=\(\dfrac{10}{56}+\dfrac{10}{140}+\dfrac{10}{260}+....+\dfrac{260}{1400}\)
Tính tổng : 10/56 + 10/140 + 10/260...+10/1400
