Bạn xem lại đề bài nhé. Với \(a=1,b=9\) thì \(111a+25b=336⋮12\) nhưng \(9a+13b=126⋮̸12\). Mình nghĩ đề bài là chứng minh \(9a+3b⋮12\). Vì \(111a+25b⋮12\) nên \(108a+24b+3a+b⋮12\) hay \(3a+b⋮12\) hay \(9a+3b⋮12\).

Công thức hiển thị không rõ ràng. Bạn nên viết lại đề nhé.

Lời giải:

$27^x+9^x=9^{25}$

$(3^3)^x+(3^2)^x=(3^2)^{25}$

$3^{3x}+3^{2x}=3^{50}$

$3^{3x+2x}=3^{50}$

$3^{5x}=3^{50}$

$\Rightarrow 5x=50$

$\Rightarrow x=10$

         C =   1 - 2 + 2² - 2³ + 2⁴ -...+ 2²⁰²²

       2C =       2 - 2² + 2³ - 2⁴ +...- 2²⁰²² + 2²⁰²³

2C + C = 2²⁰²³ + 1

      3C = 2²⁰²³ + 1

       C = \(\dfrac{2^{2023}+1}{3}\)

\(\dfrac{-13}{5}< \dfrac{7}{x}< \dfrac{-9}{4}\)

\(\Rightarrow\dfrac{-4}{9}< \dfrac{x}{7}< \dfrac{-5}{13}\)

\(\Rightarrow\dfrac{-4.7.13}{7.9.13}< \dfrac{9.13x}{7.9.13}< \dfrac{-5.7.9}{7.9.13}\)

\(\Rightarrow\dfrac{-364}{7.9.13}< \dfrac{117x}{7.9.13}< \dfrac{-315}{7.9.13}\)

\(\Rightarrow117x\in\left\{-363;-362;...;-314\right\}\)

\(\Rightarrow117x=-351\)

\(\Rightarrow x=-3\)

Vậy phân số đó là \(\dfrac{-7}{3}\)

tui học lớp 4 chứ có phải lớp 7 đâu.

\(M=2a-\dfrac{5b}{a}-3b\)

\(\dfrac{a}{b}=\dfrac{3}{5}\Rightarrow a=\dfrac{3}{5}b\) và \(\dfrac{b}{a}=\dfrac{5}{3}\)

\(\Rightarrow M=2.\dfrac{3}{5}b-5.\dfrac{5}{3}-3b\)

\(\Rightarrow M=\dfrac{6}{5}b-3b-\dfrac{25}{3}\)

\(\Rightarrow M=\left(\dfrac{6}{5}-3\right)b-\dfrac{25}{3}\)

\(\Rightarrow M=\dfrac{-9}{5}b-\dfrac{25}{3}\)

`@` `\text {Ans}`

`\downarrow`

\(\dfrac{253}{-254}=\dfrac{-253}{254}\)

\(-\dfrac{1234}{1232}=\dfrac{-617}{616}\)

Ta có: \(\dfrac{617}{616}>1\) ; \(\dfrac{253}{254}< 1\)

`=>`\(\dfrac{617}{616}>\dfrac{253}{254}\)

`=>`\(\dfrac{-617}{616}< \dfrac{-253}{254}\)

Vậy, \(\dfrac{253}{-254}>\dfrac{-1234}{1232}\).

\(MSC=254.1232\)

\(\dfrac{253}{-254}=\dfrac{-253}{254}=\dfrac{-253.1232}{254.1232}=\dfrac{\text{-311696}}{254.1232}\)

\(\dfrac{-1234}{1232}=\dfrac{-1234.254}{254.1232}=\dfrac{\text{-313436}}{254.1232}\)

mà \(\dfrac{\text{-313436}}{254.1232}< \dfrac{\text{-311696}}{254.1232}\)

\(\Rightarrow\dfrac{-1234}{1232}< \dfrac{253}{-254}\)

\(\)

cần gấp!!!

lâu thế!!

`@` `\text {Ans}`

`\downarrow`

\(\dfrac{1}{3}\div x=-\dfrac{5}{7}-\left(-\dfrac{2}{3}\right)\)

`=>`\(\dfrac{1}{3}\div x=-\dfrac{5}{7}+\dfrac{2}{3}\)

`=>`\(\dfrac{1}{3}\div x=-\dfrac{1}{21}\)

`=>`\(x=\dfrac{1}{3}\div\left(-\dfrac{1}{21}\right)\)

`=> x = -7`

Vậy `x = -7.`

1/3:x=-5/7- -2/3
1/3:x=-1/21
      x=1/3: (-1/21)
      x=-7