a=㏒2 3 b=㏒4 9
2^5a-4b=2^(5log2 3-4log4 9)
=2^(log2 3^5-4*(1/2)log2 9)
=2^(log2 3^5-2*(1/2)log2 9^2)
=2^(log2 3^5-log2 9^2)
=2^log2 (3^5/9^2)
=3^5/9^2
=3简单一点嘛。。通俗点。。初中还没学loglog 代表取对数 是高中学的。由2^a=3得 (2^a)^5=2^5a=3^5由4 ^b=9得2^2b=9则2^4b=9^2所以 2^(5a-4b)=2^5a/2^4b=3^5/9^2=3