C = 1 - \(\dfrac{\left(x+3\right)\left(x+5\right)}{2}\)

C = 1 - \(\dfrac{x^2+5x+3x+15}{2}\)

C = 1 - \(\dfrac{x^2+\left(5x+3x\right)+15}{2}\)

C = 1 - \(\dfrac{x^2+8x+16-1}{2}\)

C = 1 - \(\dfrac{\left(x^2+2.x.4+4^2\right)}{2}\) + \(\dfrac{1}{2}\)

C = (1 + \(\dfrac{1}{2}\)) -  \(\dfrac{\left(x+4\right)^2}{2}\)

C =  \(\dfrac{3}{2}\)- \(\dfrac{\left(x+4\right)^2}{2}\)

Vì (\(x+4\))² ≥ 0 \(\forall\) \(x\) ⇒ - \(\dfrac{1}{2}\)(\(x+4\))² ≤ 0 ∀ \(x\)

    ⇒ \(\dfrac{3}{2}\) - \(\dfrac{\left(x+4\right)^2}{2}\) ≤ \(\dfrac{3}{2}\) dấu bằng xảy ra khi \(x+4\) = 0 ⇒ \(x=-4\)

Vậy giá trị lớn nhất của biểu thức C là \(\dfrac{3}{2}\) xảy ra khi \(x=-4\) 

(-43). 16 + (-84).43 - (-43)

= - 43.(16 + 84 - 1)

= -43.(100 - 1)

= -43 . 99

= - 4257 

= - 

218,55

`(2345 + 45) - 2345`

`= 2345 + 45 - 2345`

`= (2345 - 2345) + 45`

`= 0 + 45`

`=45`

thưc hien cac phep tinh

`(2x - 5)(2x + 1) = (2x - 5)(x + 4)`

`(2x - 5)(2x + 1) - (2x - 5)(x +4) = 0`

`(2x - 5)[(2x + 1) - (x + 4)]=0`

`(2x - 5)(2x + 1 - x - 4) = 0`

`(2x - 5)(x - 3) = 0`

\(\left[{}\begin{matrix}2x-5=0\\x-3=0\end{matrix}\right.\\ \left[{}\begin{matrix}2x=5\\x=3\end{matrix}\right.\\ \left[{}\begin{matrix}x=\dfrac{5}{2}\\x=3\end{matrix}\right.\)

(2\(x-5\)).(2\(x+1\)) = (2\(x-5\)).(\(x+4\))

(2\(x-5\))(2\(x+1\)) - (\(2x-5\)).(\(x+4\)) = 0

(2\(x-5\))[2\(x+1\) - \(x-4\)] = 0

 (2\(x-5\)).[(2\(x-x\)) - (4 - 1)] = 0

  (2\(x\) - 5).[\(x\) - 3] = 0

   \(\left[{}\begin{matrix}2x-5=0\\x-3=0\end{matrix}\right.\)

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

Vậy \(x\) \(\in\) {\(\dfrac{5}{2}\); 3} 

tính từng bước nha

5² - 2x = -11

25 - 2x = - 11

 2x       = 25 - ( - 11 )

 2x        =   36

   x        =  36 : 2

   x        = 18

Vẫy x = 18

`5^2 - 2x = -11`

`=> 25 - 2x = -11`

`=> 2x = 25 - (-11) `

`=> 2x = 25 + 11`

`=> 2x = 36`

`=> x = 36 : 2`

`=> x = 18`

Vậy ...

\(\dfrac{16}{2^x}\) = 2

\(\dfrac{2^4}{2^x}\) = 2

2^\(4-x\) = 2¹

 4 - \(x=1\)

      \(x=4-1\)

     \(x=2\)

Vậy \(x=3\) 

Cách hai: \(\dfrac{16}{2^x}\) = 2

                2\(^x\) = 16 : 2

               2\(^x\) = 8

                2\(^x\) = 2³

                  \(x=3\)

Vậy \(x=3\) 

`270 - (3^2 xx 2 + 7^15 : 7^13)`

`= 270 - (9 xx 2 + 7^(15-13))`

`= 270 - (18 + 7^2)`

`= 270 - (18 + 49)`

`= 270 - 67`

`= 203`

270 - ( 3² . 2 + 7¹⁵ + 7¹³ )

= 270 - ( 9 . 2 + 7² )

= 270 - ( 18 + 49 )

= 270 - 67

= 203