Question

True?

Answer 1

good (this is one of the identities you have to memorize)

Answer 2

from the chart you provided , either b or D ?

Answer 3

try using

cos(2* alpha) = 2cos^2(alpha) -1

plug in 6x for alpha and see what you end up with

Answer 4

right but we need to apply this to the context of our problem

cos(12x) = 2cos^2(6x) - 1

if we add 1 to each side

cos(12x) = 2cos^2(6x)

leading us to answer choice A