An air-standard thermodynamic cycle consists of isentropic compression with pressure ratio R, isobaric heat addition, isentropic expansion and isobaric heat rejection. The ratio of specific heats is denoted by γ, which expression gives the thermal efficiency:a.1-R(γ-1)/ γb.1- R(1-γ)c.1-R(1- γ)/ γd.1-R(γ-1)