# Complex product

1. Nov 14, 2008

### kasse

$$Re [e^{iE_{0}t/\hbar} \cdot e^{-iE_{1}t/\hbar}] = Re[ e^\frac{it}{\hbar}(E_{0}-E_{1})] = cos \frac{t}{\hbar}(E_{o}-E_{1})$$

Correct?

Last edited: Nov 14, 2008
2. Nov 14, 2008

### Staff: Mentor

Check your multiplication. You ended up with two terms, each with two factors. You should have ended up with four terms, each with two factors.

Another approach is to multiply the two exponentials first before converting them to cos X + i sin X. Remember that e^A * e^B = e^(A + B).

3. Nov 14, 2008

### kasse

I've updated it. Is this what you meant?

4. Nov 14, 2008

### Staff: Mentor

That's what I meant in "another approach." Also, your answer looks to be correct this time.