Where are they
hiding the e,
the ln,
and the e^{x} ? 


Start by finding the keys you will be using:
e (to the first power) can be found above
the division key.
ln has its own key on the left side of the
keypad.
e^{x} is found above the ln
key.
Remember: e
is an irrational number, approximately 2.71828183,
named after the 18th century Swiss mathematician, Leonhard Euler.
f (x) =
e^{x}, is
called the natural
exponential function.
f (x) = ln x,
is called the natural logarithmic
function.
These two functions are inverses of one another.
When composed, these two
functions return the starting value,
thus creating the identity function, y = x. 