A = \(\dfrac{25}{1\times6}\) + \(\dfrac{25}{6\times11}\) + \(\dfrac{25}{11\times16}\)+\(\dfrac{25}{16\times21}\)+ \(\dfrac{25}{26\times31}\)

A = 5 \(\times\) ( \(\dfrac{5}{1\times6}\)+\(\dfrac{5}{6\times11}\)+\(\dfrac{5}{11\times16}\)+\(\dfrac{5}{16\times21}\)+\(\dfrac{5}{26\times31}\))

A = 5 \(\times\) ( \(\dfrac{1}{1}\) - \(\dfrac{1}{6}\) + \(\dfrac{1}{6}\) - \(\dfrac{1}{11}\)+ \(\dfrac{1}{11}\)- \(\dfrac{1}{16}\)+ \(\dfrac{1}{16}\)- \(\dfrac{1}{21}\)+ \(\dfrac{1}{26}\)- \(\dfrac{1}{31}\))

A = 5 \(\times\)( 1 - \(\dfrac{1}{31}\))

A = 5 \(\times\) \(\dfrac{30}{31}\)

A = \(\dfrac{150}{31}\)

ư

a) \(\dfrac{5}{1\cdot6}+\dfrac{5}{6\cdot11}+...+\dfrac{5}{26\cdot31}\)

\(=1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+...+\dfrac{1}{26}-\dfrac{1}{31}\)

\(=1-\dfrac{1}{31}\)

\(=\dfrac{30}{31}\)

b) \(\dfrac{4}{11\cdot16}+\dfrac{4}{16\cdot21}+...+\dfrac{4}{61\cdot66}\)

\(=\dfrac{4}{5}\cdot\left(\dfrac{5}{11\cdot16}+\dfrac{5}{16\cdot21}+...+\dfrac{5}{61\cdot66}\right)\)

\(=\dfrac{4}{5}\cdot\left(\dfrac{1}{11}-\dfrac{1}{16}+\dfrac{1}{16}-...+\dfrac{1}{61}-\dfrac{1}{66}\right)\)

\(=\dfrac{4}{5}\cdot\left(\dfrac{1}{11}-\dfrac{1}{66}\right)\)

\(=\dfrac{4}{5}\cdot\dfrac{5}{66}\)

\(=\dfrac{4}{66}\)

\(=\dfrac{2}{33}\)

a) A = 5²/(1.6) + 5²/(6.11) + ... + 5²/(26.31)

= 5.[5/(1.6) + 5/(6.11) + ...+ 5/(26.31)]

= 5.(1 - 1/6 + 1/6 - 1/11 + ... + 1/26 - 1/31)

= 5.(1 - 1/31)

= 5.30/31

= 150/31

b) B = 4/(11.16) + 4/(16.21) + ... + 4/(61.66)

= 4/5 .[5/(11.16) + 5/(16.21) + ... + 5/(61.66)]

= 4/5.(1/11 - 1/16 + 1/16 - 1/21 + ... + 1/61 - 1/66)

= 4/5.(1/11 - 1/66)

= 4/5 . 5/66

= 2/33

    ( 25 x 36 ) : 9 + 450 - 75 - 25

= 900 : 9 + 450 - 75 - 25

= 100 + 450 - 75 - 25

= 100 + ( 450 - 75 - 25 )

= 100 + 350

= 450

Vậy : ( 25 x 36 ) : 9 + 450 - 75 - 25 = 450 

bằng 450 bạn nhé

tk mình nha

( 25x36) :9+450-75-25

= 900:9+450-74-25

=100+450-75-25

=550-75-25

=475-25

=450

gạch mấy số giống nhau đi bạn

bạn làm cụ thể cho mình vs

`a)25/(x+1)-1 1/6=-1/3-0,5`

`=>25/(x+1)=-1/3-1/2+1+1/6`

`=>25/(x+1)=1/3`

`=>75=x+1`

`=>x=74`

Vậy `x=74`

`b)(2x+25 3/5)^2-9/25=0`

`=>(2x+128/5)=9/25`

`**2x+128/5=3/5`

`=>2x=-125/5=-25`

`=>x=-25/2`

`**2x+128/5=-3/5`

`=>2x=-131/5`

`=>x=-131/10`

Giải:

a) \(\dfrac{25}{x+1}-1\dfrac{1}{6}=\dfrac{-1}{3}-0,5\) 

              \(\dfrac{25}{x+1}=\dfrac{-5}{6}+\dfrac{7}{6}\) 

              \(\dfrac{25}{x+1}=\dfrac{1}{3}\) 

\(\Rightarrow1.\left(x+1\right)=25.3\)  

\(\Rightarrow x+1=75\) 

\(\Rightarrow x=75-1\) 

\(\Rightarrow x=74\) 

b) \(\left(2x+25\dfrac{3}{5}\right)^2-\dfrac{9}{25}=0\) 

              \(\left(2x+\dfrac{128}{5}\right)^2=0+\dfrac{9}{25}\) 

             \(\left(2x+\dfrac{128}{5}\right)^2=\dfrac{9}{25}\) 

\(\Rightarrow\left[{}\begin{matrix}\left(2x+\dfrac{128}{5}\right)^2=\left(\dfrac{3}{5}\right)^2\\\left(2x+\dfrac{128}{5}\right)^2=\left(\dfrac{-3}{5}\right)^2\end{matrix}\right.\) 

\(\Rightarrow\left[{}\begin{matrix}2x+\dfrac{128}{5}=\dfrac{3}{5}\\2x+\dfrac{128}{5}=\dfrac{-3}{5}\end{matrix}\right.\) 

\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{-25}{2}\\x=\dfrac{-131}{10}\end{matrix}\right.\) 

Chúc bạn học tốt!

Cách 1

= 625 : 125

= 5

Cách 2

= 625 : 25 :5

= 25 : 5

= 5

Đúng 100%

Đúng 100%

Đúng 100%

625 : (25 x 5)

= 625 : 125

= 5

~~~ ủng hộ tớ nha ~~~

~~~` thank you ~~~ ☺ ..

= 625 : 125 

= 5 

chỉ vậy thôi được ko

\(A=\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+...+\frac{1}{26.31}\)

    \(=1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+\frac{1}{16}+...+\frac{1}{26}-\frac{1}{31}\)

    \(=1+\left(-\frac{1}{6}+\frac{1}{6}\right)+\left(-\frac{1}{11}+\frac{1}{11}\right)+...+\left(-\frac{1}{26}+\frac{1}{26}\right)-\frac{1}{31}\)

 \(=1-\frac{1}{31}=\frac{31-1}{31}\)

\(=\frac{30}{31}\)

Vậy \(A=\frac{30}{31}\)

\(A=\frac{5}{1.6}+\frac{5}{6.11}+\frac{5}{11.16}+...+\frac{5}{26.31}\)

\(\Rightarrow A=\frac{1}{1}-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+...+\frac{1}{26}-\frac{1}{31}\)

\(\Rightarrow A=\frac{1}{1}-\frac{1}{31}\)

\(\Rightarrow A=\frac{30}{31}\)

giải thích: vận tốc của người đi xe đạp là: 60 x 25% = 15 (km/h)

Ta có : abc * 25 = 9abc

abc * 25 = 9000 + abc

9000 = abc * ( 25 - 1 )

9000 = abc * 24

abc = 9000 : 24

abc = 375

Vậy 9abc = 9375

Cảm ơn bạn nhiều nha!!!!