若lg2=a,lg3=b,则log9 40
问题描述:
若lg2=a,lg3=b,则log9 40
答
log9(40)
=lg40/lg9
=lg(2²×10)/lg3²
=(lg2²+lg10)/(2lg3)
=(2lg2+1)/(2lg3)
=(2a+1)/(2b)