A(α+β)/β B:β/(α+β) C.(αβ)/(α+β) D.(α+β)/(αβ)
A.T1+T2-T1*T2 B.(T1*T2)/(T1+T2) C.(T1+T2)/(T1*T2) D.T1+T2-(T1*T2)/(T1+T2)
A.R1+R2-R1*R2 B.(R1*R2)/(R1+R2) C.(R1+R2)/(R1*R2)