Question

PROVE THE IDENTITY
cos(3t)= cost(1-4sin^2t)

Answer 1

@Mertsj

Answer 2

do you start by changing left to cos(2t+t)?

Answer 3

yes

Answer 4

so the left side youd follow the cosine identity? and right side youd keep same?

Answer 5

@Mertsj what do you do then

Answer 6

yes

Answer 7

what?

Answer 8

Then replace cos(2t) with 1-2sin^2t

Answer 9

and then?

Answer 10

sin2t with 2sintcost?

Answer 11

yes

Answer 12

then?

Answer 13

can someone help me with my problem

Answer 14

@shubham1 Stop with the hijacking of another person's post.

Answer 15

@shubham this isnt where youu ask for help. you put your question in the question box.

Answer 16

yeah, dont do that. this is my post.

Answer 17

@Mertsj sorry, so you were saying?

Answer 18

how do you simplify the left then

Answer 19

Simplify and then factor out cos t

Answer 20

so..

Answer 21

@shamil98 ;D

Answer 22

Then you are done.

Answer 23

She needs more guidance

Answer 24

@Mertsj
Can you finish my question.
Will give medal

Answer 25

please stop that.

Answer 26

if i factor out cos t can you show me cuz im a little stuck

Answer 27

\[\cos (2t+t)=\cos 2t \cos t-\sin 2t \sin \sin t=(1-2\sin ^2t) \cos t-2\sin t \cos t \sin t=\]
\[\cos t-2\sin ^2t \cos t-2\sin ^2t \cos t=\cos t-4\sin ^2t \cos t=\cos t(1-4\sin ^2t)\]

Answer 28

thank you!!!

Answer 29

yw