A polynomial function P(x) with degree 5 increases in the interval and and decreases in the interval (1,3). Given that and , find P'(6).
In this problem, I have recognised that 2 is an inflection point and the derivative will be of the form: .
But I am unable to understand why is double root of the derivative (i.e. why is ?). It's not making sense to me. I need help with that part.