Question

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

Answer 1

$f:[0,4\pi ]\to [0,\pi ],f\left(x\right)=co{s}^{-1}\left(cosx\right)$
$\Rightarrow$ point A, B, C satisfy $f\left(x\right)=\frac{10-x}{10}$
Hence, 3 points