If $A=\left\{x:-\frac{2}{5} \leq x \leq \frac{\pi-2}{5}\right\}, B=\{y:-1 \leq y \leq 1\}$ and $f(x)=\cos (5 x+2)$ then the mapping $f: A \rightarrow B$ is

both one-one and onto

Let $t=5 x+2$, then $A=\{t: 0 \leq t \leq \pi\}$

∴  $f(t)= \cos t$ which is bijective in $[0, \pi]$

Hence, f(x) is bijective.

Hence (3) is the correct answer.