Given a tangent plane with equation at point Q= (a, b) z = f(a, b)
show this plane is parallel to the normal vector
t = <0,0,1>
at point Q.
Provide written explanation.

-2 is the right

let's first notice, the center of the hyperbola is at the origin, since the focus points are equidistantly 3 units away from the origin, that also means that the distance "c" from the center to either focus is 3.

it should also be notable that, the traverse axis for this hyperbola is vertical, or namely over the y-axis and therefore, the positive fraction will be the one with y-variable.

the traverse "a" component or distance from the center to either vertex is not 2, is more than 2, so we can safely put it at √5 ≈ 2.24.