Question

how do i find the vertex of this parabola?
y=-3x^2

Answer 1

Vertex is at (0,0)

Answer 2

the vertex of parabola \[\huge y=a(x-\color{blue}{h})^2+\color{red}{k}\]
will be (h,k).
So compare your equation \[\huge y=-3(x-\color{blue}{0})^2+\color{red}{0}\]
with the above one, and find the vertex, can you ?