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26 tháng 2 2019

H=10/56+10/140+10/260+....+10/1400

H=5/28+5/70+5/130+....+5/700

3H/5=3/4.7+3/7.10+3/10.13+...+3/25.28

3H/5=1/4-1/7+1/7-1/10+1/10-1/13+....+1/25-1/28

3H/5=1/4-1/28

3H/5=3/14

H=3/14.5/3

H=5/14

Vậy H=5/14

25 tháng 4 2016

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

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

16 tháng 4 2015

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

14 tháng 2 2016

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

14 tháng 2 2016

khó @gmail.com

\(A=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)

\(A=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}\)

\(\frac{3A}{5}=\frac{3}{4\times7}+\frac{3}{7\times10}+\frac{3}{10\times13}+...+\frac{3}{25\times28}\)

\(\frac{3A}{5}=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\)

\(\frac{3A}{5}=\frac{1}{4}-\frac{1}{28}\)

\(\frac{3A}{5}=\frac{3}{14}\)

\(A=\frac{3}{14}\times\frac{5}{3}\)

\(A=\frac{5}{14}\)

3 tháng 6 2017

a) F = \(\frac{1}{25.27}+\frac{1}{27.29}+\frac{1}{29.31}+...+\frac{1}{73.75}\)

F = \(\frac{1}{2}.\left(\frac{1}{25}-\frac{1}{27}\right)+\frac{1}{2}.\left(\frac{1}{27}-\frac{1}{29}\right)+\frac{1}{2}.\left(\frac{1}{29}-\frac{1}{31}\right)+...+\frac{1}{2}.\left(\frac{1}{73}-\frac{1}{75}\right)\)

F = \(\frac{1}{2}.\left(\frac{1}{25}-\frac{1}{27}+\frac{1}{27}-\frac{1}{29}+\frac{1}{29}-\frac{1}{31}+...+\frac{1}{73}-\frac{1}{75}\right)\)

F = \(\frac{1}{2}.\left(\frac{1}{25}-\frac{1}{75}\right)\)

F = \(\frac{1}{2}.\frac{2}{75}\)

F = \(\frac{1}{75}\)

b) G = \(\frac{15}{90.94}+\frac{15}{94.98}+\frac{15}{98.102}+...+\frac{15}{146.150}\)

G = \(\frac{15}{4}.\frac{4}{90.94}+\frac{15}{4}.\frac{4}{94.98}+\frac{15}{4}.\frac{4}{98.102}+...+\frac{15}{4}.\frac{4}{146.150}\)

G = \(\frac{15}{4}.\left(\frac{1}{90}-\frac{1}{94}\right)+\frac{15}{4}.\left(\frac{1}{94}-\frac{1}{98}\right)+\frac{15}{4}.\left(\frac{1}{98}-\frac{1}{102}\right)+...+\frac{15}{4}.\left(\frac{1}{146}-\frac{1}{150}\right)\)

G = \(\frac{15}{4}.\left(\frac{1}{90}-\frac{1}{94}+\frac{1}{94}-\frac{1}{98}+\frac{1}{98}-\frac{1}{102}+...+\frac{1}{146}-\frac{1}{150}\right)\)

G = \(\frac{15}{4}.\left(\frac{1}{90}-\frac{1}{150}\right)\)

G = \(\frac{15}{4}.\frac{1}{225}\)

G = \(\frac{1}{60}\)

3 tháng 6 2017

<br class="Apple-interchange-newline"><div id="inner-editor"></div>12.4 +14.6 +...+198.100 

=12 (22.4 +24.6 +...+298.100 )

<br class="Apple-interchange-newline"><div id="inner-editor"></div>=12 (12 14 +14 16 +...+198 1100 )

<br class="Apple-interchange-newline"><div id="inner-editor"></div>=12 (12 14 +14 16 +...+198 1100 )

<br class="Apple-interchange-newline"><div id="inner-editor"></div>=12 (12 1100 )=12 .49100 =49200 

1056 +10140 +10260 +...+101400 =53 (

5 tháng 2 2022

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@py. Hello, hihi

17 tháng 1 2016

M=5/28+5/70+...+5/700=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

6 tháng 3 2016

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 :D