Question

de moivre's theorem
if a=cos 2alpha + i sin 2alpha
b= cos 2beta + i sin 2beta prove,
a-b/a+b = i tan (alpha-beta)

Answer 1

seriously need some help

Answer 2

anyone ?

Answer 3

My advice is to give alpha and beta values: so lets say alpha=30 and beta=60
put it into the equation and solve, if it comes out the same on both sides (like 2=2) then you have proven it to be true

Answer 4

hmmm... let me see if that works..thank you for replying.

Answer 5

no problem, just remember if you have to prove a theory the best way is to plug in random numbers. hope this helps :)

Answer 6

it is not happening since I have "i" left , which is a problem.