已知3^x=2,2^x=1,3^y=4,2^y=5,求12^(3x-y)的值

12^(3x-y)
=12^3x/12^y
=3^3x*4^3x/3^y*4^y
=(3^x)^3*(2^2)^3x/[3^y*(2^2)^y]
=(3^x)^3*(2^x)^6/[3^y*(2^y)^2]
=2^3*1^6/[4*5^2]
=8*1/[4*25]
=8/100
=2/25