Question

More trig troubles

Answer 1

Verify the identity.

cos 4x + cos 2x = 2 - 2 sin2 2x - 2 sin2 x

Answer 2

\[\cos4x+\cos2x= 2-2\sin^2(2x)-2\sin^2(x)\]

Answer 3

yes that is it

Answer 4

cos2x=1-2sin^2(x)

Answer 5

okay so \[\cos4x+\cos2x=1-2\sin^2x+\cos2x\]

Answer 6

yes thats one way.

Answer 7

or I meant it to be 2sin^2(2x)

Answer 8

1-2sin^2(2x)+cos2x

Answer 9

now subtract the cos2x from both sides. unless you are doing a proof

Answer 10

yeah i figured that.

Answer 11

I'm doing a proof

Answer 12

well then you can only minipulate one side at a time. you can change both but you cant subtract or multiply anything from both sides.

Answer 13

just try to get them to look alike.

Answer 14

does 1-2sin^2(2x) turn into cos4x by any chance?

Answer 15

maybe.

Answer 16

yes I believe so

Answer 17

wait its a proof lets do this a different way.

Answer 18

but that was right becasue you do the more compllicated side to get the smaller side

Answer 19

i guess so. i think it should be ok.

Answer 20

so then \[\cos(2u)=1-\sin^2(u) \]

Answer 21

u=2x

Answer 22

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

Answer 23

i meant to put "2sin^2(2x)"

Answer 24

does that make sense?

Answer 25

much! thank you!

Answer 26

Yw!