This function, called the
logarithmic function, is defined by
logb : R+ → R
x → logb x = y   if by = x
As before if the base b = 10, we say it
is common logarithms and if b = e, then
we say it is natural logarithms Often
natural logarithm is denoted by ln In this
chapter, log x denotes the logarithm
function to base e, i e