Question

Let $f:[0,4\pi ]\to [0,\pi ]$ be defined by $f\left(x\right)={\cos }^{-1}\left(\cos x\right)$. The number of points $x\in [0,4\pi ]$ satisfying the equation $f\left(x\right)=\frac{10-x}{10}$ is

Answer 1

The number of point of intersection of $\frac{10-x}{10}$ and ${\cos }^{-1}\left(\cos x\right)$ is $3$ for $x\in [0,4\pi ]$