where a is the length of the semi-major axis and b is the length of the semi-minor axis.
Given that the vertex (-6, 0) and co-vertex (0, 4), we can see that the semi-major axis is 6 units long, and the semi-minor axis is 4 units long.
Therefore, the equation in standard form of the ellipse is:
which simplifies to:
Thus, the equation in standard form of the ellipse centered at the origin with a vertex (-6,0) and co-vertex (0,4) is: