已知log 2=a log 7=b 求 log8 9.8的值
问题描述：
已知log 2=a log 7=b 求 log8 9.8的值
答
log 8 = log 2x2x2 = 3 log 2 = 3a
log 9.8 = log 98/10
= log 49*2/10
= log 7*7*2/10
=( 2 log 7 + log 2) - log 10
= (2b + a ) - 1
log 8 9.8
= log 9.8 / log 8
=(2 log 7 + log 2 - log 10)/(3 log 2)
=(2b + a - 1)/(3a)