Which of the following functions are onto functions?
A function f:A→B is onto if every element of the co-domain has a pre-image.
i.e., f is onto if range equals co-domain.
We know that the range of the functions sin x and cos x is [-1,1]. Since range equals co-domain, both of these functions are onto.
Similarly, we can check for the other three functions and we’ll find that all functions are onto.