Science:Math Exam Resources/Courses/MATH100/December 2011/Question 05 (c)/Hint 1

The first derivative was needed in part (b) and has already been computed. Take the derivative of that function:

${\begin{aligned}f'(x)&={\frac {6}{5}}x^{-4/5}+{\frac {6}{5}}x^{1/5}\\&={\frac {6(x+1)}{5x^{4/5}}}\end{aligned}}$