对数题不明白怎么得的!

loga b=x ,则a^x=b,即a的x次方为b,只是一个逆运算,
lg 0.01
=-2,10^(-2)=1/100=0.01;
log9 ⒏⒈
=2, 9^2=81;
log0.4 ⒈
=0, 0.4^0=1;
log15 ⒈⒌
=1 15^1=15;
log7 ⒊⒋⒊
=3 7^3=343;
log2.5 6.25
=2 2.5^2=6.25;
log3 243
=5 3^5=243.