Answer:
[tex]-1.5[/tex]
Step-by-step explanation:
We have been given an equation [tex]y=3x^2+9x[/tex]. We are asked to find the x-coordinate of the vertex of the parabola for our given equation.
We will use formula [tex]\frac{-b}{2a}[/tex] to finc the x-coordinate of vertex of given parabola.
Upon substituting our given values in above formula we will get,
[tex]\frac{-9}{2*3}[/tex]
[tex]\frac{-3*3}{2*3}[/tex]
[tex]\frac{-3}{2}[/tex]
[tex]-1.5[/tex]
Therefore, the x-coordinate of vertex of given parabola is [tex]-1.5[/tex].
