tính tong 10/56 + 10/140 + 10/260 + ..... + 10/1400
Tính tổng:A=10/56+10/140+10/260+.........+10/1400
\(A=\dfrac{5}{28}+\dfrac{5}{70}+\dfrac{5}{130}+...+\dfrac{5}{700}\)
\(\dfrac{3A}{5}=\dfrac{3}{4.7}+\dfrac{3}{7.10}+\dfrac{3}{10.13}+...+\dfrac{3}{25.28}\)
\(\dfrac{3A}{5}=\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{25}-\dfrac{1}{28}\)
\(\dfrac{3A}{5}=\dfrac{1}{4}-\dfrac{1}{28}=\dfrac{3}{14}\)
⇒ \(A=\dfrac{5}{14}\)
tính: 10/56+10/140+10/260+...+10/1400
bài này bạn chỉ cần tách mẫu ra là làm được thôi
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
Đặt S= 5/28 + 5/70 + 5/130 +.....+5/700
= 5/4.7 + 5/7.10 + ......+ 5/ 25.28
3S/5=1/4-1/7+1/7-1/10+.....+1/25-1/28
3S/5=1/4-1/28
3S/5=3/14
3S=3/14x5
3S=15/14
S=15/14x1/3
S=15/42
tính nhanh 10/56+10/140+10/260+...+10/1400
Vừa nãy mk k cho bạn đấy,Lê Mai Uyên ạ!
Đáp số là\(\frac{5}{14}\)
Bạn nhớ k cho mk nha!
Chúc bạn học giỏi!
Tính B=1-10/56-10/140-10/260-...-10/1400
Tính :
10/56+10/140+10/260+...+10/1400
= 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 S=10/56+10/140+10/260+..............+10/1400
S=10/56+10/140+10/260+....+10/1400
S=5/28+5/70+5/130+....+5/700
3S/5=3/4.7+3/7.10+3/10.13+...+3/25.28
3S/5=1/4-1/7+1/7-1/10+1/10-1/13+....+1/25-1/28
3S/5=1/4-1/28
3S/5=3/14
S=3/14.5/3
S=5/14
Vậy S=5/14
S=10/56+10/140+10/260+...........+10/1400
S=5/28+5/70+5/130+........+5/700
3S/5=3/4.7+3/7.10+3/13.10+.........+3/25.28
3S/5=1/4-1/7+1/7-1/10+1/10-1/13+.........+1/25-1/28
3S/5=1/4-1/28
3S/5=3/14
S=3/14.5/3
S=5/14
S=5/28+5/70+5/130+.....+5/700
S=5/4x7+5/7x10+5/10x13+.....+5/25x28
Sx3/5=3/4x7+3/7x10+.......+3/25x28
Sx3/5=1/4-1/7+1/7-1/10+1/10+.....+1/25-1/28
Sx3/5=1/4+(1/7-1/7)+(1/9-1/9)+.....+(!/25-1/25)-1/28
Sx3/5=1/4-1/28
Sx3/5=3/14
S=3/14 : 3/5
S=5/14
Tính tổng: M=10/56+10/140+10/260+...+10/1400
M=10/56+10/140+10/260+...+10/1400
=5/28+5/70+5/130+...+5/700
=5/4.7+5/7.10+5/10.13+...+5/25.28
=5/3(3/4.7+3/7.10+3/10.13+...+3/25.28)
=5/3(1/4-1/7+1/7-1/10+1/10-1/1+...+1/25-1/28)
=5/3.(1/4-1/28)
=5/3.3/14
=5/14
\(\frac{5}{14}\) Là đúng đó bn
nhớ k cho mình nha! hjhj