Which of the following is the most effective way to increase the efficiency of the Carnot engine?

Let temperature of heat reservoir and heat sink are T1 and T2 respectively.η=1−T2T1Let T2 is reduced by ∆T, henceη1=1−T2−ΔTT1Let in other case T1 is increased by ∆T, hence, η2=1−T2T1+ΔT η1−η2=1−T2−ΔTT1−1+T2T1+ΔT η1−η2=T2T1+ΔT−T2−ΔTT1 or =T1−T2ΔT+(ΔT)2T1T1+ΔT Since T1>T2 , hence η1>η2