PreCalculus - Trigonometry: Trig Identities (31 of 57) Proof cos^2(x)=(1+cos2x)/2

In this video I will prove cos^2(x)=(1+cos2x)/2.

[khikgikhi]

Really hard to find some good videos about specific problems but i found it!

[azinakachiasonye]

Does cos^2(2x) then equal (1+cos4x)/2?

[neiichu]

Thank you very much, this video saved me !

[blazingcraft]

Does cos^2+sin^2=1 work as well? Why do we use 2cos as the basis?

[Priceygames]

(cosx)^2=cos(x×x) why did you put cos(x+x)

[rdjparker]

why do we change the negative sign of sin into a positive sign when we flip the terms at the 4th ligne ?

[mohanjha]

If possible, please improve your lighting. Can't see a thing