I'm assuming you meant to write y=-2x^2-3
There are 2 basic ways to find the vertex.
Since you're in algebra (I'm assuming) plug it into -b/2a. This will give you the x value for the turning point.
-b/2a
0/2(-2)
0
Now plug in 0 to the equation to get the y value.
y=-2(0)^2-3
y=-3
Ok so the point is (0,-3)
Best of luck!
