η=1+T2T1\eta =1+\frac{T_2}{T_1}η=1+T1T2
η=T2T1\eta =\frac{T_2}{T_1}η=T1T2
η=1−T1T2\eta =1-\frac{T_1}{T_2}η=1−T2T1
η=1−T2T1\eta =1-\frac{T_2}{T_1}η=1−T1T2
