How to judge whether a function is decreasing or increasing, odd or even, especially logarithmic function

How to judge whether a function is decreasing or increasing, odd or even, especially logarithmic function

There are several steps to find the monotonicity of a function
1. If the values X1 and X2 belong to the domain {I} and make x1f (x2), then the function decreases monotonically on {I}, if f (x1)