posted by kevin .
find the equation of a tangent line of
x^(1/4) + y^(1/4) = 4 at the point (16,16)
1/4 x^-3/4 dx + 1/4 y^-3/4 dy=0
16=(-16/16)^3/4 + b
which is a curious problem, you have to take the 4th root of a negative number, which is not a real number. End of problem, there is no line.
check my thinking.