One of the ways to write the Double Angle Identiy for Cosine is:
You can rearrange this to come to the step your book has taken.
Hi, I'm struggling to understand how to prove this:
(sin^4) T = ( 3 - 4 cos 2 T + cos 4 T ) / 8
(where T is theta)
I start on the left side and "break" this up into a square:
( sin^2 T) ^ 2
From here, my book does the following:
( 1 - cos 2 T / 2 ) ^ 2
Why?
I know sin^2 is also = 1 - cos ^ 2
How do I know to use the double angle identity?? It doesn't seem to apply if I'm just working with sin^2 T?
Thanks!
Hello, Snowcrash!
Prove: .
I start on the left side and "break" this up into a square: .
From here, my book does the following: .
Why?
I know: .
How do I know to use the double angle identity?
How else are you going to change your
. . into an expression with . ?