因为2^m=5所以2^3m=(2^m)^3=5^3=125因为2^n=3所以2^2n=(2^n)^2=3^2=92^(3m-2n)=(2^3m)/(2^2n)=125/9
2^m=5,2^n=3, 2^(3m-2n)=(2^m)*(2^m)*(2^m)/((2^n)*(2^n)）=5*5*5/（3*3）=125/9
2的3m-2n=(2的m次方)^3/(2的n次方)^2=27/25
