log(3)15乘以log(5)15=log3(3*5)*log5(3*5)=(log3(3)+log3(5))*(log5(3)+log5(5))=(1+log3(5))*(log5(3)+1)=1+log3(5)*log5(3)+log3(5)+log5(3)=1+(ln3/ln5)*(ln5/ln3)+log3(5)+log5(3)=2+log3(5)+log5(3)