Questions in IIP2 derivation

I'm reading <Effective IM2 products estimation for two-tone and W-CDMA modulated blockers in 3GPP directconversion receivers> written by Ali-Ahmad W. In IIP2 derivation, I have something which I cannot understand.

1. A2/R is the equivalent power of A × cos(ω1t) or A × cos(ω1t) +A × cos(ω2t)? Why?
2. Why can cos[(ω1-ω2)t] and cos[(ω1+ω2)t] be transformed to 1/2R

Regards
Diego