Perpendicular line to the Surface

[τheory]

Homework Statement

Consider the line perpendicular to the surface z=x^2+y^2 at the point where x = −1 and y = 2 Find a vector parametric equation for this line in terms of the parameter t.

The Attempt at a Solution

I wasn't quite sure how to go about with this problem so I just went along with the following ideas. I first took the gradient of the function at that point:

0=x^2+y^2-z
∇F(x,y,z)= <2x,2y,-1>
∇F(-1,2,0)= <-2,4,-1>

Then I constructed the vector parametric equation of the line at that point:

L(t) = P + t∇F
L(t) = <-1,2,0> + t<-2,4,-1>

Afterwards, I submitted this equation, only finding that it was incorrect; can someone explain to me what went wrong here?

 

[LCKurtz]

When $x=-1$ and $y=2$, $z$ isn't zero.

 

[τheory]

Wow haha that was a horrible miscalculation on my part. Thanks for pointing that out!