Question

I have to prove this is in an identity. I dont think this one is so if someone could double check for me I would really appreciate it!!

cos3t= cos^3(t)sin(t)- sin^3(t)cos(t)
does the cubes make this a doable problem?

Answer 1

start out with
cos(3t) = cos( 2t + t )

Answer 2

cos 3t=cos(t+2t) now expand this using the identity cos(a+b)=cos a cos b-sin a sin b

Answer 3

@theee_queenbee

Answer 4

sorry I am having connection issues :( but when I tried it on paper I got cos(t)sin^2(t)-sin(t)cos^2(t)

Answer 5

so what am I doing wrong?

Answer 6

@Princer_Jones

Answer 7

@theee_queenbee are you proceeding in this manner?

Answer 8

no I was looking at another identity. thats why I was confused. ok so now I have
cos(t) (2cos^2(t)-1) - sin(t) (2sin(t)cos(t)) ( im visual so I write it out the long way unfortunately)

Answer 9

what should we prove??

Answer 10

Do you know this how to prove?? cos 3x= 4 cos^3 (x) - 3cos x @theee_queenbee