Answer:
There is no short answer.
Step-by-step explanation:
To find to intervals which f(x) increases or decreases, we first need to find it's derivative.
The function is increasing when it's value is > 0 and decreasing when it's value is < 0.
If we take a look at this graph, cosx+sinx is positive when they are both positive or when cosx is greater then sinx on the negative part.
I hope this answer helps.
