Question

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

Answer 1

$f :[0,4 \pi] \rightarrow[0, \pi], f ( x )=\cos ^{-1}(\cos x ) $
$\Rightarrow $ point $ A , B , C$ satisfy $ f ( x )=\frac{10- x }{10}$
Hence, $3$ points