Half and Double-angle formulas

[SilverKing]

Hi everyone,


I know the following formulas:



How do they become like these?

 

[stapel]

I know the following formulas:
View attachment 3763

How do they become like these?

View attachment 3764

What do you get when you replace "2x" with "x"? What adjustments do you logically make?

 

[SilverKing]

I've got the idea, thank you stapel

I was confused though ^^"