Science:Math Exam Resources/Courses/MATH100/December 2018/Question 05 (c)/Statement

Let $f(x)=x^{\frac{9}{7}}+\frac{9x^{\frac{2}{7}}}{2}.$ (c) Find the intervals on which $f(x)$ is concave up and the intervals on which $f(x)$ is concave down.