What Happens to Average Power in an RLC Circuit at Resonance?

[8614smith]

Homework Statement

4.) Determine the average power in an RLC circuit. Derive an expression for the resonance frequency in terms of L and C. Is the average power a maximum or a minimum at the resonance frequency?

Homework Equations

The Attempt at a Solution

I have circled in red the part that is giving me trouble, all the rest of the solution i can do, is that part some identity or rule i am missing?

 

[8614smith]

this picture is probably a bit easier to see...