Question

log784(1/4)+log784(1/7) 

Answer 1

$log_{784}frac{1}{4}+log_{784}frac{1}{7}=log_{784}frac{1}{28}=log_{28^2}28^{-1}=-frac{1}{2}$

Answer 2

Log784(1/4)+log784(1/7)=log28