Definition:Exponential Function/Real/Differential Equation

Definition
Let $\exp: \R \to \R_{>0}$ denote the (real) exponential function. The exponential function can be defined as the unique solution $y = f \left({x}\right)$ to the first order ODE:


 * $\dfrac {\d y} {\d x} = y$

...satisfying the initial condition $f(0) = 1$.

That is, the defining property of $\exp$ is that it is its own derivative. The number $\exp x$ is called the exponential of $x$.