\(a,3x^2-3x\left(x-2\right)=36\\ \Leftrightarrow3x^2-3x^2+6x=36\\ \Leftrightarrow6x=36\\ \Leftrightarrow x=6\\ b,5x\left(4x^2-2x+1\right)-2x\left(10x^2-5x+2\right)=-36\\ \Leftrightarrow20x^3-10x^2+5x-20x^3+10x^2-4x+36=0\\ \Leftrightarrow\left(20x^3-20x^3\right)+\left(-10x^2+10x^2\right)+\left(5x-4x\right)=-36\\ \Leftrightarrow x=-36\)

\(\begin{array}{l}a){\rm{ }}3{x^2}-{\rm{ }}3x\left( {x{\rm{ }}-{\rm{ }}2} \right){\rm{ }} = {\rm{ }}36\\ \Leftrightarrow 3{x^2}-{\rm{ [}}3x.x + 3x.( - 2)] = 36\\ \Leftrightarrow 3{x^2} - (3{x^2} - 6x) = 36\\ \Leftrightarrow 3{x^2} - 3{x^2} + 6x = 36\\ \Leftrightarrow 6x = 36\\ \Leftrightarrow x = 36:6\\ \Leftrightarrow x = 6\end{array}\)

Vậy x = 6

\(\begin{array}{l}b){\rm{ }}5x\left( {4{x^2}-{\rm{ }}2x{\rm{ }} + {\rm{ }}1} \right){\rm{ }}-{\rm{ }}2x\left( {10{x^2}-{\rm{ }}5x{\rm{ }} + {\rm{ }}2} \right){\rm{ }} = {\rm{ }} - 36\\ \Leftrightarrow 5x.4{x^2} + 5x.( - 2x) + 5x.1 - [2x.10{x^2} + 2x.( - 5x) + 2x.2] =  - 36\\ \Leftrightarrow 20{x^3} - 10{x^2} + 5x - (20{x^3} - 10{x^2} + 4x) =  - 36\\ \Leftrightarrow 20{x^3} - 10{x^2} + 5x - 20{x^3} + 10{x^2} - 4x =  - 36\\ \Leftrightarrow (20{x^3} - 20{x^3}) + ( - 10{x^2} + 10{x^2}) + (5x - 4x) =  - 36\\ \Leftrightarrow x =  - 36\end{array}\)

Vậy x = -36

\(\dfrac{x}{y}=\dfrac{-3}{4}\)

⇒\(\dfrac{x}{-3}=\dfrac{y}{4}\) 

⇒\(\dfrac{2x}{-6}=\dfrac{3y}{12}\)

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

\(\dfrac{2x}{-6}=\dfrac{3y}{12}=\dfrac{3y-2x}{12-\left(-6\right)}=\dfrac{36}{18}=2\)

⇒\(\left\{{}\begin{matrix}x=2.-3=-6\\y=2.4=8\end{matrix}\right.\)

`(2x+5)(2x-7)-(2x-3)^2=36`

`<=>4x^2-14x+10x-35-(4x^2-12x+9)=36`

`<=>4x^2-4x-35-4x^2+12x-9=36`

`<=>8x-44=36`

`<=>8x=80`

`<=>x=10`

Vậy `S={10}`

Ta có: \(\left(2x+5\right)\left(2x-7\right)-\left(2x-3\right)^2=36\)

\(\Leftrightarrow4x^2-14x+10x-35-\left(4x^2-12x+9\right)=36\)

\(\Leftrightarrow4x^2-4x-35-4x^2+12x-9=36\)

\(\Leftrightarrow8x-44=36\)

\(\Leftrightarrow8x=80\)

hay x=10

Vậy: S={10}

hình như đề sai bạn ạ

đề sai bạn ơi

​

\(A.\left(2a+1\right)^2-4\left(a+2\right)^2=9\\ \left(2a+1-2a-4\right)\left(2a+1+2a+4\right)=9\)

\(-3\left(4a+5\right)=9\\ -12a-15=9\\ -12a=24\\ a=-2\)

\(B.\left(a+3\right)^2-\left(a-4\right)\left(a+8\right)=1\\ a^2+6a+9-\left(a^2+8a-4a-32\right)=1\)

\(a^2+6a+9-a^2-4a+32=1\\ 2a=-40\\ a=-20\)

a) \(-45:5.\left(-3-2x\right)=3\)

\(-9.\left(-3-2x\right)=3\)

\(-3-2x=\left(3:-9\right)\)

\(-3-2x=\dfrac{-1}{3}\)

\(-2x=-3-\dfrac{1}{3}\)

-2x=\(\dfrac{-10}{3}\)

\(x=\dfrac{-10}{3}:-2\)

\(x=\dfrac{5}{3}\)

b) 

3x - 28 = x + 36

<=> 3x - x = 36 + 28

<=> 2x = 64

<=> x = 32

Vậy x = 32

c) 

(-12)2.x = 56 + 10.13.x

144.x = 56 + 130.x

144x – 130 x = 56

14x = 56

x = 56: 14

x = 4

Vậy x = 4

\(a,-45:5\cdot\left(-3-2x\right)=3\\ \Leftrightarrow-9\cdot\left(-3-2x\right)=3\\ \Leftrightarrow-2x-3=-\dfrac{1}{3}\\ \Leftrightarrow2x+3=\dfrac{1}{3}\\ \Leftrightarrow2x=-\dfrac{8}{3}\\ \Leftrightarrow x=-\dfrac{4}{3}\\ b,3x-28=x+36\\ \Leftrightarrow2x=64\\ \Leftrightarrow x=32\\ c,\left(-12\right)^2x=56+10\cdot13x\\ \Leftrightarrow144x=56+130x\\ \Leftrightarrow14x=56\\ \Leftrightarrow x=4\)

c) x( 2x - 3 ) - 2( 3 - 2x) =0

\(\Leftrightarrow x\left(2x-3\right)+2\left(2x-3\right)=0\)

\(\Leftrightarrow\left(x+2\right)\left(2x-3\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x+2=0\\2x-3=0\end{array}\right.\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-2\\x=\frac{3}{2}\end{array}\right.\)

d) 25x² - 36 =0

\(\Leftrightarrow\left(5x\right)^2-6^2=0\)

\(\Leftrightarrow\left(5x-6\right)\left(5x+6\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}5x-6=0\\5x+6=0\end{array}\right.\)

\(\Leftrightarrow x=\pm\frac{6}{5}\)

a) \(x\left(2x-3\right)-2\left(3-2x\right)=0\)

=> \(\left(2x-3\right)\left(x+2\right)=0\)

=>\(\left[\begin{array}{nghiempt}2x-3=0\\x+2=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=\frac{3}{2}\\x=-2\end{array}\right.\)

b) \(25x^2-36=0\)

\(\Leftrightarrow\left(5x-6\right)\left(5x+6\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}5x-6=0\\5x+6=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=\frac{6}{5}\\x=-\frac{6}{5}\end{array}\right.\)