Equation to a level surface Could someone please help me with the following question:

Consider the function $g(x,y,z)=\ln(x^2-y+z^2)$. Find an equation of the level surface of the function through the point $(-1,2,1)$ which does not have $\ln$. Hint: first find $g(-1,2,1).$

When I sub in the points I get $$g(-1,2,1)=\ln(1-2+1)=\ln(0)=\text{undefined}$$. Where am I going wrong?
Thanks,
bbelson01

$$\ln(x^2-y+z^2)=\ln(x_0^2-y_0+z_0^2)$$
can be rewritten
$$y=x^2+z^2+(y_0-x_0^2-z_0^2).$$
It remains the same paraboloid of revolution, with the apex moving along the axis $y$.
