\(H=\dfrac{5}{4x7}+\dfrac{5}{7x10}+\dfrac{5}{10x13}+....+\dfrac{5}{25x28}\\ =>\dfrac{3}{5}xH=\dfrac{3}{4x7}+\dfrac{3}{7x10}+\dfrac{3}{10x13}+....+\dfrac{3}{25x28}\\ =>\dfrac{3}{5}xH=\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+...+\dfrac{1}{25}-\dfrac{1}{28}=\dfrac{1}{4}-\dfrac{1}{28}=\dfrac{6}{28}=\dfrac{3}{14}\\ =>H=\dfrac{5}{14}\)

Ta có: \(H=\dfrac{5}{28}+\dfrac{5}{70}+\dfrac{5}{130}+...+\dfrac{5}{700}\)

\(H=5\left(\dfrac{1}{4x7}+\dfrac{1}{7x10}+\dfrac{1}{10x13}+...+\dfrac{1}{25x28}\right)\)

\(\Rightarrow3H=15\left(\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+...+\dfrac{1}{25}-\dfrac{1}{28}\right)\)

\(\Rightarrow3H=15\left(\dfrac{1}{4}-\dfrac{1}{28}\right)=\dfrac{45}{14}\)

\(\Rightarrow H=\dfrac{15}{14}\)

22/25.(9/11-3/2)+4/1

= 22/25 . ( -15/22) + 4/1

= -3.5 + 4/1

= 17/5

`22/25 . (9/11 -3/2) + 4/1`

`=22/25 . (9/11 -3/2) + 4`

`=22/25 . (18/22 - 33/22) + 4`

`=22/25 . (-15)/22 + 4`

`=(22xx(-15))/(25xx22) +4`

`= (-15)/25 + 4`

`=(-3)/5 + 4`

`=(-3)/5 + 20/5`

`= (-3+20)/5`

`=17/5`

`#LeMichael`

giúp mik với ạ

mik đang cần ạ

Ta có: \(A=\dfrac{3}{1x4}+\dfrac{3}{4x7}+\dfrac{3}{7x10}+...+\dfrac{3}{100x103}\)

\(=\dfrac{1}{1}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{100}-\dfrac{1}{103}\)

\(=1-\dfrac{1}{103}=\dfrac{102}{103}\)

Vậy \(\dfrac{102}{103}\)

`C=(4-1)/(1xx4)+(7-4)/(4xx7)+(10-7)/(7xx10)+....+(103-100)/(100x103)`

`=(4)/(1xx4)-(1)/(1xx4)+(7)/(4xx7)-(4)/(4xx7)+(10)/(7xx10)-(7)/(7xx10)+....+(103)/(100xx103)-(100)/(100xx103)`

`=(1)/(1)-(1)/(4)+(1)/(4)-(1)/(7)+(1)/(7)-(1)/(10)+...+(1)/(100)-(1)/(103)`

`=1-(1)/(103)=(102)/(103)`

Chu vi mảnh đất :

`100xx4=400(m)`

Diện tích hình mảnh đất :

`100xx100=10000(m^2)`

Diện tích thửa ruộng :

`50xx30=1500(m^2)`

Diện tích còn lại :

`10000-1500= 8500(m^2)`

Diện tích trồng lúa :

`8500xx 1/5 = 1700(m^2)`

Đ/s...

`#LeMichael`

`25 xx 15 + 47 xx 95 + 25 xx 38 - 47 xx 70`

`= [ 25 xx ( 15 + 38)] + [ 47 xx ( 95 - 70)]`

`= [25 xx 53]+ [ 47 xx 25]`

`=25 xx 53 + 47xx 25`

`=25 xx ( 53 + 47)`

`=25 xx 100`

`=2500`

`#LeMichael`

`25.15+47.95+25.38-47.70`

`=25.(15+38)+47.(95-70)`

`=25.53+47.25`

`=25.(53+47)`

`=25.100`

`=2500`

27.(62+37)+73.(43+56)

= 27.99 + 73 . 99

= 99 .( 27+73)

= 99. 100

= 9900

`27.(62 + 37) + 73.(43+56)`

`=27.99 + 73 . 99`

`=99 . (27 + 73)`

`=99 . 100`

`=9900`

`#LeMichael`

\(B=\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+...+\dfrac{2}{99\times101}\)

\(B=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+....+\dfrac{1}{99}-\dfrac{1}{101}\)

\(B=1-\dfrac{1}{101}=\dfrac{100}{101}\)

\(B=\dfrac{3-1}{1x3}+\dfrac{5-3}{3x5}+\dfrac{7-5}{5x7}+\dfrac{9-7}{7x9}+...+\dfrac{101-99}{99x101}\\ =\dfrac{3}{1x3}-\dfrac{1}{1x3}+\dfrac{5}{3x5}-\dfrac{3}{3x5}+\dfrac{7}{5x7}-\dfrac{5}{5x7}+\dfrac{9}{7x9}-\dfrac{7}{7x9}+...+\dfrac{101}{99x101}-\dfrac{99}{99x101}\\ =\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+...+\dfrac{1}{99}-\dfrac{1}{101}\\ 1-\dfrac{1}{101}=\dfrac{100}{101}\)