\(\left(6-x\right)\left(2x+9\right)=45\\ \Rightarrow2x\left(6-x\right)+9\left(6-x\right)=45\\ \Rightarrow12x-2x^2+54-9x-45=0\\ \Rightarrow-2x^2+3x+9=0\\ \Rightarrow2x^2-3x-9=0\\ \Rightarrow\left(2x^2-6x\right)+\left(3x-9\right)=0\\ \Rightarrow2x\left(x-3\right)+3\left(x-3\right)=0\\ \Rightarrow\left(x-3\right)\left(2x+3\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=3\\x=-\dfrac{3}{2}\end{matrix}\right.\)
(6 - x)(2x + 9) = 45
-2x^2 + 3x + 9 = 0
(3 - x)(2x + 3) = 0
x = 3 hoặc x = -3/2
\(\Leftrightarrow12x+54-2x^2-9x-45=0\)
\(\Leftrightarrow-2x^2+3x+9=0\)
\(\Leftrightarrow2x^2-3x-9=0\)
\(\Leftrightarrow2x^2-6x+3x-9=0\)
\(\Leftrightarrow\left(x-3\right)\left(2x+3\right)=0\)
hay \(x\in\left\{3;-\dfrac{3}{2}\right\}\)
(6-x)(2x+9)=45
⇔12x + 54 - 2x2 - 9x = 45
⇔ 2x2 - 3x - 9 = 0
⇔\(\left\{{}\begin{matrix}x=3\\x=-\dfrac{3}{2}\end{matrix}\right.\)
