- #1
DEMJ
- 44
- 0
Homework Statement
[tex]e^{i\theta_1}e^{i\theta_2} = e^{i(\theta_1 + \theta_2)}}[/tex]
Homework Equations
The Attempt at a Solution
For some reason every I multiply [tex](cos\theta_1 + isin\theta_1)(cos\theta_2 + isin\theta_2)[/tex] I am getting
[tex](cos\theta_1 cos\theta_2 + sin\theta_1 sin\theta_2) + i(sin\theta_1 cos\theta_2 + cos\theta_1 sin\theta_2)[/tex]
according to my book the first part should be [tex](cos\theta_1 cos\theta_2 - sin\theta_1 sin\theta_2)[/tex]
what am I missing here? Is it some basic fundamental from calculus I have forgotten?
What I am doing is [tex]cos\theta_1 cos\theta_2 - (isin\theta_1)(isin\theta_2) = cos\theta_1 cos\theta_2 - i^2 sin\theta_1 sin\theta_2[/tex] since [tex]i^2 = -1[/tex] that makes it positive. But this can't be right because both the book and my notes from class cannot be wrong. So please enlighten me =]