1. The problem statement, all variables and given/known data Find the equation of the normal line of function f(x,y) = x^2+y^2-1 through points (2,1,4) 2. Relevant equations (x-xo)/f_x = (y-yo)/f_y = (z-zo)/f_z 3. The attempt at a solution so... f_x = 2x = 4 f_y = 2y = 2 f_z = ??? I don't know how to solve for f_z.... here is random stuff I was doing that *might* be related? f(x,y) - z = 0 f(x,y) = z = 4 yeah.. any math guru wanna show this grasshopper the way?