( 3x/7 + 1 ) : (-4 ) = -1/28

 3x/7 + 1           = -1/28 x (-4 ) 

(3x/7 + 1           = 1/7

3x/7                  = 1/7  - 1

3x/7                  = -6/7

Suy ra 3x = -6

            x = -6 : 3

            x = -2

=>3x/7+1=-1/28x(-4)

=>3x/7+1=1/7

=>3x/7=1/7-1

=>3x/7=-6/7

=>3x=6

=>x=6:3=2

k mình đi

Ta có : (3x/7+1) : (-4) = -1/28

3x/7+1 = -1/28 . (-4)

3x/8 = 1/7

Do đó 3x.7/56 = 8/56

Suy ra 3x.7=8

Suy ra 3x =8 : 7

Suy ra 3x = 8/7

Suy ra x = 8/7 : 3

Do đó x = 8/21

(3x - 24).3 = 2.54

(3x - 24).3 = 108

3x – 24 = 108 : 3

3x – 24 = 36

3x = 36 + 24

3x = 60

X = 60 : 3

X = 20

(3x-24).3=2.54

9x-72=108

9x      =108-72

9x       =36

x=36:4

x=9

nếu đúng thì tích đúng cho mình nha

\(A=3x-x^2=-\left(x^2-\frac{2.3.x}{2}+\frac{9}{4}\right)+\frac{9}{4}\)\(=\frac{9}{4}-\left(x-\frac{3}{2}\right)^2\le\frac{9}{4}\)

Vậy GTLN của A là \(\frac{9}{4}\)đạt được khi x = \(\frac{3}{2}\)

`@` `\text {Ans}`

`\downarrow`

Ta có: \(\dfrac{x-1}{2}=\dfrac{y+3}{4}=\dfrac{z-5}{6}\)

\(\Rightarrow\dfrac{3x-3}{6}=\dfrac{4y+12}{16}=\dfrac{5z-25}{30}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{3x-3}{6}=\dfrac{4y+12}{16}=\dfrac{5z-25}{30}\)`=`\(\dfrac{\left(5z-25\right)-\left(3x-3\right)-\left(4y+12\right)}{30-6-16}\)

`=`\(\dfrac{5z-25-3x+3-4y-12}{8}\)

`=`\(\dfrac{\left(5z-3x-4y\right)+\left(-25+3-12\right)}{8}\)

`=`\(\dfrac{50-34}{8}\)`=`\(\dfrac{16}{8}=2\)

`=>`\(\dfrac{x-1}{2}=\dfrac{y+3}{4}=\dfrac{z-5}{6}=2\)

`=>`\(\left\{{}\begin{matrix}x=2\cdot2+1=5\\y=2\cdot4-3=5\\z=2\cdot6+5=17\end{matrix}\right.\)

Vậy, `x,y,z` lần lượt là `5; 5; 17.`

Lời giải:

a. $145-135(x-2)^2=10$

$135(x-2)^2=145-10=135$

$(x-2)^2=135:135=1=1^2=(-1)^2$
$\Rightarrow x-2=1$ hoặc $x-2=-1$

$\Rightarrow x=3$ hoặc $x=1$

--------------------------

b.

$x\in Ư(36); x\geq 12$

$\Rightarrow x\in\left\{12; 18; 36\right\}$

c.

$x-1=B(9)\Rightarrow x-1\in\left\{0; 9; 18; 27; 36; 45;54;.....\right\}$

$\Rightarrow x\in\left\{1; 10; 19; 28; 37;46; 55;....\right\}$

Mà $25< x< 50$ nên $x\in\left\{28; 37; 46\right\}$

\(a,\Rightarrow2x^2-18x-2x^2=0\\ \Rightarrow-18x=0\Rightarrow x=0\\ b,\Rightarrow2x^2-5x-12+x^2-7x+10=3x^2-17x+20\\ \Rightarrow5x=22\Rightarrow x=\dfrac{22}{5}\)