Critical Point(s) of a Multivariable Function

[johnhuntsman]

Homework Statement

Find the critical points of f.
f(x,y)=2+\sqrt{3(x-1)^2+4(y+1)^2}

Homework Equations

For f_x(x,y) I get:
f_x(x,y)=0+\frac{1*6(x-1)}{2\sqrt{3(x-1)^2+4(y+1)^2}}=\frac{3(x-1)}{\sqrt{3(x-1)^2+4(y+1)^2}}
For f_y(x,y) I get:
f_y(x,y)=0+\frac{1*8(y+1)}{2\sqrt{3(x-1)^2+4(y+1)^2}}=\frac{4(y+1)}{\sqrt{3(x-1)^2+4(y+1)^2}}

The Attempt at a Solution

Solving both of these for x and y when set equal to 0, gets me x = 1 and y = -1. However neither of these functions exist when x and y equal those values. Does the original function still have a critical point at (x,y) = (1,-1)?

Additionally, when I put the function into Wolfram Alpha it says that it has no critical points.

 

[voko]

What is the definition of the critical point?