Finding Cartesian equation of parametric surface.

[Ral]

Homework Statement

Find the Cartesian equation of the parametric surface: [2cos(t)cos(s), 3sin(s), sin(t)cos(s)]

Find eqn. of the tangent plane when S = 0, t = pi/2

Homework Equations

The Attempt at a Solution

I'm not quite sure what to do. All I've done is squared each term, which gave me.

$$4cos^2(t)cos^2(s)$$
$$9sin^2(s)$$
$$sin^2(t)cos^2(t)$$

 

[Donaldos]

$$x=2\cos t\cos s$$

$$y=3\sin s$$

$$z=\sin t \cos s$$

Can't you find $$\alpha$$ and $$\beta$$ so that $$x^2+\alpha y^2 + \beta z^2= constant$$?