We have a parabola
y = -x^2
The vertex is at x=0
If x =0, y = 0^2 so y =0 (0,0) is the vertex
Lets pick a point to the right
x=1 y = -1^2 =- 1 so when x=1 y = -1 (1, -1)
Again another point to the right
x=2 y = -2^2 = - 4 so when x=2 y = -4 (2, -4)
We know that the parabola is symmetric across the vertex, but we can prove it
x= -1 y = -( -1) ^2 = -(1) = -1 ( -1,-1)
x = -2 y = -(-2)^2 = -4 ( -2, -4)