Hello all

I have a couple of questions.

First, if the first derivative of a function is a quadratic can I show that the function has no stationary points by showing that the discriminant of the first derivative is less than zero?

Second, how do I go about finding the range of the values ofafor which

y = x - (a/x) has no stationary points.

I know the answer is thatais greater than or equal to zero, but I don't know how to get there.

Thank you.