# Surface area of parametric equation

1. Aug 4, 2009

### Pete_01

1. The problem statement, all variables and given/known data
For the surface with parametric equations r(st)=<st, s+t, s-t>, find the equation of the tangent plane at (2,3,1).
Find the surface area under the restriction s^2 + t^2 <=(lessthanorequalto) 1

2. Relevant equations

3. The attempt at a solution
I already figured out the equation of the tangent plane: -2x+3y-z=4, but I am not sure how to find the surface area? I want to use the SA equation |rs x rt| integrated from ds 0 to 1 and dt 0 to 2pi but i am not having much luck. Any ideas?

2. Aug 6, 2009

### Billy Bob

If you are integrating with dA=ds dt, from ds 0 to 1, then dt would be 0 to $$\sqrt{1-s^2}$$. Try converting the double integral to polar coordinates with dA=r dr d_theta.