= 5/28+5/70+5/130+...+5/700
=5/3.(3/4.7+3/7.10+3/10.13+...+3/25.28)
=5/3.(1/4-1/7+1/7-1/10+1/10-1/13+...+1/25-1/28)
=5/3.(1/4-1/28)=5/3.3/14=5/14
k mik nha
Tính tổng:A=10/56+10/140+10/260+.........+10/1400
tính: 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
tính nhanh 10/56+10/140+10/260+...+10/1400
tính tong 10/56 + 10/140 + 10/260 + ..... + 10/1400
Tính B=1-10/56-10/140-10/260-...-10/1400
tính tổng S=10/56+10/140+10/260+..............+10/1400
Tính tổng: M=10/56+10/140+10/260+...+10/1400
