log2(25)*log3(4)*log5(9)=lg25/lg2*lg4/lg3*lg9/lg5 (换底公式)=lg5^2/lg2*lg2^2/lg3*lg3^2/lg5=2lg5/lg2*2lg2/lg3*2lg3/lg5 =2(lg5/lg2)*2(lg2/lg3)*2(lg3/lg5)=8*1=8