Hello there. To solve this question, we'll have to remember some properties about trigonometric functions and sum of angles.
Given the following functions, we want to express them as a function of an acute angle:

First, remember the following properties:

That we can prove easily knowing some properties of sum of angles:

For the second, we use the same formula for sum of angles for cosines

In this case, notice that

It is easy to see that

Such that the function expressing this as a function of an acute angle is

And for the cosine, we'll get

Again we see that

Such that we get the function

There are the answer to this question.