tinh tong M=10\56+10\140 +.............+10\1400
tinh tổng :M=10/56+10/140+......+10/1400
tính tong 10/56 + 10/140 + 10/260 + ..... + 10/1400
tinh nhanh
10/56+10/140+10/260+...+10/1400
tính M = 10/56+10/140+10/416+.....+10/1400
tinh nhanh
H=\(\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)
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
tính M=10/56+10/140+1/26+...+10/1400
tính
M = 10/56 + 10/140 + 10/260 + . . . . . + 10/1400
@Thành Tò Văn
Đầu tiên rút gọn M trước
M= 5/28 + 5/70 +.....+10/700
= 5/(4.7)+5/(7.10)+....5/(25.28)
3M= 5( 1/4 - 1/7 +1/7-1/10+......+1/25-1/28)
3M= 5 (1/4-1/28)
3M=15/14
M= 5/14
Ta có :
\(M=\dfrac{10}{56}+\dfrac{10}{140}+\dfrac{10}{260}+...................+\dfrac{10}{1400}\)
\(M=\dfrac{5}{28}+\dfrac{5}{70}+\dfrac{5}{130}+...............+\dfrac{5}{700}\)
\(M=\dfrac{5}{4.7}+\dfrac{5}{7.10}+\dfrac{5}{10.13}+..............+\dfrac{5}{25.28}\)
\(\dfrac{3}{5}M=\left(\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+............+\dfrac{1}{25}-\dfrac{1}{27}\right)\)
\(\dfrac{3}{5}M=\dfrac{1}{4}-\dfrac{1}{27}\)
\(\dfrac{3}{5}M=\dfrac{3}{14}\)
\(M=\dfrac{3}{14}:\dfrac{3}{5}=\dfrac{5}{24}\)
\(\dfrac{10}{56}+\dfrac{10}{140}+\dfrac{10}{260}+...+\dfrac{10}{1400}=\dfrac{5}{28}+\dfrac{5}{70}+\dfrac{5}{130}+...+\dfrac{5}{700}\)
\(=\dfrac{5}{4.7}+\dfrac{5}{7.10}+\dfrac{5}{10.13}+...+\dfrac{5}{25.28}\)
\(=\dfrac{5}{3}.\left(\dfrac{3}{4.7}+\dfrac{3}{7.10}+\dfrac{3}{10.13}+...+\dfrac{3}{25.28}\right)\)
\(=\dfrac{5}{3}.\left(\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{25}-\dfrac{1}{28}\right)\)
\(=\dfrac{5}{3}.\left(\dfrac{1}{4}-\dfrac{1}{28}\right)=\dfrac{5}{3}.\dfrac{3}{14}=\dfrac{5}{14}\)
Chúc bạn học tốt!!!
tính tổng M=\(\dfrac{10}{56}+\dfrac{10}{140}+\dfrac{10}{260}+....+\dfrac{260}{1400}\)