Question

The number of solution of $\cos (x+\frac{\pi }{4})=\frac{1}{5}$ in $[0,2\pi ]$ is

Answer 1

Draw the graph of $y=\cos (x+\frac{\pi }{4})$ and $y=\frac{1}{5}$


The number of solution is same as number of points of intersection of the both curves,
Therefore, from graph the number of solutions is $2.$