'y' is 1/e ... about 0.3679 . It's not a function of anything, and it doesn't change
in response to a change in anything else.
'y' is what's known as a
'number' or a 'constant', and its derivative with respect
to anything is
zero.
When graphed, the equation [ y = e^-1 ] is a straight horizontal line. Its
slope is zero, and it intercepts the y-xis at the point (0, 0.3679...). (rounded).
