`@` `\text {Ans}`

`\downarrow`

\(\dfrac{2}{3}+\left[\dfrac{4}{5}x-\dfrac{11}{15}\right]=\dfrac{5}{9}\)

`=>`\(\dfrac{4}{5}x-\dfrac{11}{15}=\dfrac{5}{9}-\dfrac{2}{3}\)

`=>`\(\dfrac{4}{5}x-\dfrac{11}{15}=-\dfrac{1}{9}\)

`=>`\(\dfrac{4}{5}x=-\dfrac{1}{9}+\dfrac{11}{15}\)

`=>`\(\dfrac{4}{5}x=\dfrac{28}{45}\)

`=>`\(x=\dfrac{28}{45}\div\dfrac{ 4}{5}\)

`=>`\(x=\dfrac{7}{9}\)

Vậy, `x = 7/9.`

\(\left(\dfrac{3}{4}-3x\right)\cdot\left(1+4x\right)=0\)

`=>`\(\left[{}\begin{matrix}\dfrac{3}{4}-3x=0\\1+4x=0\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}3x=\dfrac{3}{4}\\4x=-1\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}x=\dfrac{1}{4}\\x=-\dfrac{1}{4}\end{matrix}\right.\)

Vậy, `x \in {1/4; -1/4}.`

\(\dfrac{-2}{7}+\dfrac{2}{3}:x=\dfrac{-1}{5}\)

⇒\(\dfrac{2}{3}:x=\dfrac{-1}{5}-\dfrac{-2}{7}=\dfrac{3}{35}\)

⇒\(x=\dfrac{2}{3}:\dfrac{3}{35}=\dfrac{70}{9}\)

ai giúp mik với ak mik cần gấp

\(\dfrac{1}{1.4}+\dfrac{1}{4.2}+\dfrac{1}{2.8}+\dfrac{1}{8.4}+\dfrac{1}{4.16}+\dfrac{1}{16.8}\)

= \(\dfrac{1}{4}.\left(1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\right)\)

= \(\dfrac{1}{4}.\left(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}\right)\)

= \(\dfrac{1}{4}.\dfrac{3}{2}\left(1+\dfrac{1}{4}+\dfrac{1}{16}\right)\)

= \(\dfrac{1}{4}.\dfrac{3}{2}\left(\dfrac{16}{16}+\dfrac{4}{16}+\dfrac{1}{16}\right)\)

= \(\dfrac{3}{8}.\dfrac{21}{16}\)

= \(\dfrac{63}{128}\)

`@` `\text {Ans}`

`\downarrow`

`100 - 2(x - 4) = 20`

`=> 2(x - 4) = 100 - 20`

`=> 2(x - 4) = 80`

`=> x - 4 = 80 \div 2`

`=> x - 4 = 40`

`=> x = 40 + 4`

`=> x = 44`

Vậy, `x = 44.`

`@` `\text {Kaizuu lv uuu}`

100 - 2(x-4) = 20

⇒ 2(x-4)= 100-20=80

⇒ x-4 = 80:2 = 40

⇒ x= 40+4=44

cứu

Tỉ số phần trăm của 15 k và 120 k là:

          15 : 120 = 0,125 

          0,125 = 12,5%

Giá trị của 4 dấu ? là 12,5% 

Viết kết quả dưới dạng luỹ thừa thì phép tính này bằng \(a^{1000}\) nhé.

\(3^3\cdot3^4\cdot3^5\)

\(=3^{3+4+5}\)

\(=3^{12}\)

$3^3\cdot 3^4\cdot 3^5$

$=3^{3+4+5}$

$=3^{12}$

\(\dfrac{2}{5}-9-\dfrac{7}{2}\)

\(=\dfrac{2}{5}-\dfrac{9}{1}-\dfrac{7}{2}\)

\(=\left(\dfrac{2}{5}-\dfrac{9}{1}\right)-\dfrac{7}{2}\)

\(=\left(\dfrac{2}{5}-\dfrac{45}{5}\right)-\dfrac{7}{2}\)

\(=-\dfrac{43}{5}-\dfrac{7}{2}\)

\(=-\dfrac{86}{10}-\dfrac{35}{10}\)

\(=-\dfrac{121}{10}\)

Vì (x−7)(x+3)<0

⇒x−7>0; x+3<0

   x−7<0; x+3>0

⇒x>7;x<−3

   x<7;x>−3

⇒−3<x<7

Vậy −3<x<7

Vì 4<n≤7 và nϵN

⇒ n ϵ {5;6;7}

⇒ K=(n-1).(2n-1) ϵ {36;55;78}