How to calculate the Q of circuit simply ?

We can transform the serial part into parallel part, then use equation Q=ω0×R×C but it is too complicated. So how can i use some simple calculation to acquire the expression of Q,
The paper tell me Q≈1/{[Rs+ωtLs+(ω0*Lg)^2/Rfm]×ω0×Cgs}, How can i get this