# Grid Curve stuff Help!

1. May 11, 2008

### the7joker7

1. The problem statement, all variables and given/known data

Consider the parametric surface r(u, v) = <vsin(u), vcos(u), v^2>

The point (1, 1, 2) is on this surface. Find the grid curve with v constant that contains this point.

And the grid curve with u constant that contains the point.

Then find tangent vector to both grid curves at (1, 1, 2).

Find the angle between both grid curves at (1, 1, 2).

Some other stuff I can't even think about right now follows...

3. The attempt at a solution

I figured the grid curve with v constant is <sqrt(2)sin(u), sqrt(2)cos(u), sqrt(2)^2>

But then I couldn't get the one for U being constant, and this question still doesn't make too much sense to me in the first place...help!

2. May 11, 2008

### HallsofIvy

Staff Emeritus
Yes, in order that (v sin(u), vcos(u), v2) pass through (1, 1, 2), v must be $\sqrt{2}$. Therefore the curve through that point so that v is constant is, of course, $(\sqrt{2} sin(u), \sqrt{2} cos(u), 2)$.

Now that we have established that v must be $\sqrt{2}$ at the point (1, 1, 2), for what value of u is $(\sqrt{2} sin(u), \sqrt{2} cos(u), 2)= (1, 1, 2)$?

3. May 11, 2008

### the7joker7

pi/4. Thanks.