Question

1-2 sin e cos 20-2 sin 40 = cos (20)

Answer 1

No this is not the same as cos(2Ф)

Explanation:

First I changed the
`cos^(2)`Ф into 1-
`sin^(2)`Ф

I then foiled the (1-2
`sin^(2)`Ф)(1-
`sin^(2)`Ф) and that resulted in 1-
`sin^(2)`Ф-2
`sin^(2)`Ф+2
`sin^(4)`Ф

From there, I then cancelled the two 2
`sin^(4)`Ф and combined like terms and was left with 1-3
`sin^(2)`Ф

Now 1-3
`sin^(2)`Ф ≠ cos(2Ф)