sinx cosx tanx

cscx secx cotx

Divide sin^2 x

Divide cos^2 x

There must be an upper bound and a lower bound

Commonly used derivative judgments in the past

A constant function is a special case and its period is free.

The function obtained after adding, subtracting, multiplying, and dividing two periodic functions is still a periodic function.

The function obtained after adding, subtracting, multiplying, and dividing a periodic function and a non-periodic function must not be a periodic function.

odd function

even function

Multiplication (division) of two odd (even) functions is an even function

One odd and one even multiplication (division) are all odd functions

There are three possibilities: there is an upper bound but no lower bound, there is a lower bound but no upper bound, there are both upper and lower bounds (judgment depends on the actual situation).