1. ## Calc.3 plane etc.

Im trying to understand the steps to finding a point on the surface where the tangent plane is perpendicular to following tangent plane

$

x+y+z=11

$

2. The plane $x+y+x=11$ has normal vector $<1,1,1>$.

Find points on the surface at which the gradient is parallel to that vector.

3. on the surface of which vector?

4. Originally Posted by statman101
to finding a point on the surface where the tangent plane is perpendicular to following tangent plane
I have no idea what the surface is.
You posted the above problem. I assumed that you had a surface to work from.

5. Originally Posted by statman101
on the surface of which vector?
This makes no sense. A "vector" does not have a surface! If your surface is given by f(x, y, z)= constant, then $\nabla f$ is perpendicular to the surface. That vector must be parallel (so a multiple of) <1, 1, 1>. Now, what surface are you talking about?