# What Does That "Exp" Mean?

The "exp" stands for "exponential". The term "exp(x)" is the same as writing ex or e^x or "e to the x" or "e to the power of x". In this context, "e" is a universal constant, e = 2.718281828... it goes on forever but you don't need to know the value, your calculator probably has exp(x) or e^x as a function (if, as I am assuming, it is a scientific calculator).

It might become obvious to you if you see the equations written properly rather than in ascii text. Check the quick reference page,
http://www.execpc.com/~culp/rockets/qref.html

where the single stage equations are also written by way of review. It might be easier for you to understand what is meant by exp(x) when you see it written properly as ex.

The inverse of ex is ln(x), or the natural logarithm of x. So in other words, if I take the natural logarithm of ex, I get x back: in equation form ln(ex) = x, or equivalently, ln(exp(x)) = x. It works the other way around, too, exp(ln(x)) = x.

The expression 1-exp(x) means raise the number e to the x power then subtract it from 1. So you would say it "one minus e to the x".