An exponential function is a power function where the variable, x, is the exponent. In its most basic form, an exponential function is written as follows: f(x) = qx ou f(x) = expq(x).
The parameter q is the base of the exponent. It is a strictly positive real number not equal to 1.
The variation in an exponential function falls within 2 intervals:
If q = 1, then the function is constant. It is equivalent to the equation y = 1.
If q ≠ 1, the exponential function has the same asymptote with the equation y = 0
The exponential function expq(x) is a convex function that passes through the coordinates (0, 1) : ∀ q, q0 = 1.
Special Case: The exponential function with a tangent at the point (0,1) with line y = x, is the exponential function with the base e. It is written as f(x) = ex ou f(x) = exp(x).
e is an irrational number, called a Euler number or Napier number: e ≈ 2,718 281 : e = f(1).