( x + 2 ) ( x – 3 ) – x^2 + 5x – 18 3x – 9 – 2x ( x – 3 ) = 0

1 bình luận về “( x + 2 ) ( x – 3 ) – x^2 + 5x – 18 3x – 9 – 2x ( x – 3 ) = 0”

1. (x+2)(x-3)-x^2 + 5x -18

   = x.x – x.3 + 2.x – 2.3 – x^2 + 5x -18

   = x^2 – 3x + 2x – 6 – x^2 + 5x -18

   = (x^2 – x^2) – (3x – 2x – 5x) – (6 + 18)

   = 10x – 24

   3x – 9 – 2x (x-3) = 0

   => (3x – 9) – 2x(x-3) = 0

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

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

   $\Rightarrow\left[\begin{matrix} x-3=0\\ 3-2x=0\end{matrix}\right.$

   $\Rightarrow\left[\begin{matrix} x=3\\ 2x=3\end{matrix}\right.$

   $\Rightarrow\left[\begin{matrix} x=3\\ x=\dfrac{3}{2}\end{matrix}\right.$

   Vậy x \in {3; 3/2}

   #BlackStar

    

   Trả lời