1. The problem statement, all variables and given/known data How are we able to go from the first line to the second line and then the second line to the third? 2. Relevant equations Euler Identity: e^j(theta) = cos(theta) +jsin(theta) 3. The attempt at a solution This problem is more about preliminary theory in my opinion so I tried understanding how they converted the problem from trigonometric functions to exponential by analyzing the Euler Identity.