The graph of \(f'\) is shown for \(0\le x\le6\), and \(f(0)=0\).
a) Where does \(f\) have an inflection point? Explain using the graph of \(f'\).
b) Use area to find \(f(3)\).
c) Describe where \(f\) increases, decreases, is concave up, and is concave down. Give the coordinates of its inflection point and its maximum.

Hints
- What does the slope of the derivative graph tell you about the concavity of the original function?
- Areas under the derivative graph give changes in the original function.
- Use the derivative's sign to locate a maximum; use its direction of change to locate an inflection point.
Solution
1. The derivative increases until \(x=1\) and decreases afterward. Therefore \(f\) changes from concave up to concave down at \(x=1\).
2. The region under \(f'\) from \(0\) to \(3\) is a triangle with base \(3\) and height \(2\). Thus \(f(3)=f(0)+\frac{1}{2}\cdot3\cdot2=3\).
3. The area from \(0\) to \(1\) is \(1\), so the inflection point is \((1,1)\). Since \(f'>0\) for \(0<x<3\) and \(f'<0\) for \(3<x<6\), \(f\) increases, then decreases, with an absolute maximum at \((3,3)\). It is concave up on \((0,1)\) and concave down on \((1,6)\).
Answer
a) \(x=1\), where \(f'\) changes from increasing to decreasing.
b) \(f(3)=3\)
c) Increasing on \((0,3)\), decreasing on \((3,6)\); concave up on \((0,1)\), concave down on \((1,6)\). Inflection point: \((1,1)\). Absolute maximum: \((3,3)\).