The graph shows
\(f(x)=0.5x-\cos x\), \(g(x)=0.5x\), and \(h(x)=-\cos x\).
a) Identify the graph of each function.
b) Find the coordinates of all points on the graph of \(f\) in \([0, 2\pi]\) where the slope is \(0.5\).
c) Determine whether the graph of \(f\) has horizontal tangents. Give all such inputs if they exist.

Hints
- Compare the shapes and formulas of the three functions.
- Set the derivative equal to the desired slope in part b.
- A horizontal tangent requires the derivative to equal zero.
- Use the unit circle to solve the resulting sine equations.
Solution
1. The line through the origin is \(g(x)=0.5x\), the reflected cosine curve is \(h(x)=-\cos x\), and their pointwise sum is \(f(x)=0.5x-\cos x\).
2. Differentiate:
\(f'(x)=0.5+\sin x\).
For slope \(0.5\), solve
\(0.5+\sin x=0.5\),
so
\(\sin x=0\).
On \([0, 2\pi]\), the inputs are \(0\), \(\pi\), and \(2\pi\). The corresponding points are
\((0, -1)\),
\(\left(\pi, \frac{\pi}{2}+1\right)\),
and
\((2\pi, \pi-1)\).
3. Horizontal tangents satisfy
\(0.5+\sin x=0\),
so
\(\sin x=-\frac{1}{2}\).
Therefore,
\(x=\frac{7\pi}{6}+2\pi n\)
or
\(x=\frac{11\pi}{6}+2\pi n\),
where \(n\in\mathbb{Z}\).
Answer
a) \(g\) is the line through the origin, \(h\) is the reflected cosine curve, and \(f\) is their sum.
b) \((0, -1)\), \(\left(\pi, \frac{\pi}{2}+1\right)\), and \((2\pi, \pi-1)\)
c) \(x=\frac{7\pi}{6}+2\pi n\) or \(x=\frac{11\pi}{6}+2\pi n\), where \(n\in\mathbb{Z}\)