On the wikipedia page: List of trigonometric identities - Wikipedia, the free encyclopedia

the following table can be read:"

Symmetry

When the trigonometric functions are reflected from certain angles, the result is often one of the other trigonometric functions. This leads to the following identities:"

The table underneath says: Reflected in Theta=0, Reflected in Theta= pi/4, Reflected in Theta= pi/2.

I can't make head or tails of this. What I do know is that it can somehow be drawn in the unitcircle. That it can be made visible.

I can of course learn what is in the tables by heart, but I know I will quickly loose that information. I want to really understand it.

I hope some of you can clarify this for me. Thanks beforehand.