Question

Write the expression as the sine, cosine, or tangent of an angle.

cos 8x cos 2x - sin 8x sin 2x

Answer 1

sum of cosines:
cos(a+b)=cos(a)cos(b)-sin(a)sin(b)

Answer 2

is the answer cos6x?

Answer 3

I would say cos10x... the sign is opposite for the cosine

Answer 4

Can you show working ?

Answer 5

oh ok thanks. and yes i understand now. Can you help me with this too please? Find the exact value by using a half-angle identity. cos(pi/12)

Answer 6

cos(8x)cos(2x)-sin(8x)sin(2x)=cos(8x+2x)

Answer 7

the answer choices are
1/2 sqrt(1+sqrt(3)
1/2 sqrt(1-sqrt(3)
1/2 sqrt(2+sqrt(3)
1/2 sqrt(2-sqrt(3)

Answer 8

\[\cos (x)=\pm \sqrt{\frac{1+\cos(2x)}{2}}\]

Answer 9

is that a,b,c,or d?

Answer 10

Sorry, daughter needs help getting ready for school.

Answer 11

Half angle identities formula

Answer 12

substitute pi/12 in for x
\[\cos(\pi/12)=\pm \sqrt{\frac{1+\cos(2\frac{\pi}{12})}{2}}\]pi/12 is in the first quadrant, so it is the positive from the plus minus that we need here

Answer 13

I'm sorry, I don't just give answers, but I'll work with you... what do you think the next step is?

Answer 14

to simplify?

Answer 15

yes... do you know the answer to the cos inside the root?

Answer 16

\[\cos(2\frac{\pi}{12})=\cos(\frac{\pi}{6})=?\]you can look it up in your trig book under unit circle.

Answer 17

i got 1/2 sqrt(2+sqrt(3) is that correct?

Answer 18

yes

Answer 19

thanks

Answer 20

You're welcome, sorry for the delay while I took my girl to school.