log2(48)=a
log4(12)
=log4(48/4)
=log4(48)-1
=[log2(48)/log2(4)]-1
=(a/2)-1
=(a-2)/2太谢谢了，能不能再帮我看一下这道：解方程：2^(2x-1) =9两边取：lg()lg2^(2x-1)=lg9=2lg3(2x-1)=2lg3/lg22x=[2lg3+lg2]/lg2x=[lg3+(1/2)lg2]/lg2=log2(3)+(1/2)