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
Answer & explanation
Correct answer: option 3
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.