log(a)(b)表示以a为底的b的对数.
所谓的换底公式就是log(a)(b)=log(n)(b)/log(n)(a).
log3^2*log4^9=(1g2/1g3)*(1g9/1g4)
=(1g2/1g3)*(2*1g3/2*1g2)
=(1g2/1g3)*(1g3/1g2)
=1