Question

Please help! will give medal :)


Write the expression as the sine, cosine, or tangent of an angle.
Cos 107 degrees cos 42 degrees + sin 107 degrees sin 42 degrees

Answer 1

I am not sure what you really need to do here.

Answer 2

Idk thats what the instructions are, choices are a. sin 65, b. cos 65, c. cos 149, d. sin 149

Answer 3

I am thinking of sin(a+b) identities right now....

Answer 4

Oh, lets work this backwards, look at this formula below,

cos(A-B)=cos A cos B + sin A sin B

and compare to,

cos(65)=cos(107-42)=cos (107) cos (42) + sin (107) sin (42)

Answer 5

reply when you figure, it shouldn't be hard ;)

Answer 6

thanks, I think I got that one, but theres something I'm missing with the concept because I can't do the next problem either which is similar...
same instructions but
sin 5 x cos x - cos 5x sin x

Answer 7

@SolomonZelman

Answer 8

DO you have the options?

Answer 9

a. cos 6x
b. cos 4x
c. sin 6x
d. sin 4x

Answer 10

alright, look at this formula.

sin(A-B)=sin A cos B - cos A sin B

and compare to,

sin(5x)=sin(6x-x )=sin (5x) cos (x) - cos (5x) sin (x)

Answer 11

so sin 6x?

Answer 12

I am getting sin 5x

Answer 13

thats not an option :O

Answer 14

Yeah, ik, I am thinking...

Answer 15

are you sure you typed the question correctly?

Answer 16

sin 5x cos x - cos 5x sin x

Answer 17

then it's

sin(4x)=sin(5x-x )=sin (5x) cos (x) - cos (5x) sin (x)

my bad abt the 1st mistake :(

Answer 18

ohh, all good, thanks!

Answer 19

You welcome, have a good one ;)