Is it possible to have a positive exponential function that starts below zero?

I'm working on a project for my math class. We need to make an image on our calculators (Texas Instruments) using the DrawF function (which graphs functions as y=). I need an exponential function that starts below zero. From what I understand, they can't (according to my Algebra II textbook and a few Google searches).

Is it possible to draw the line I need with an exponential?

Side note: I would rather use this than, say, mushing it together with other types of equations because we need at least two exponential functions, and I can't find a better place to use them.

Answer

Multiplying an exponential function by any real number is still an exponential function

Take $$f(x) = -e^{x}$$

Then $f(0) = -1$. On the other hand if you want purely a function which is of the form $f(x) = a^x$, you will need to use complex numbers but then there's no real concept of a number being "negative"