Let's say (a,b,c) is the closest point on the curve, The line from (a,b,c) to (1,1,0) is (a-1,b-1,c)
The normal to the surface at (a,b,c) is ∇S(at a,b,c) = (2a, 6b, -2c). these lines must be the same, so
2a/(a-1) = 6b/(b-1) = -2c/c = -2 Solve for a and b --> (1/2, 1/4, c)
You can now find c by solving c = ±sqrt(a2+3b2 - 1/3) (the sign doesn't matter here)
You can then calculate d = sqrt((a-1)2+(b-1)2 + c2) should be around .957