Exponential function - Wikipedia
https://en.wikipedia.org/wiki/Exponential_functionThe graph of is upward-sloping, and increases faster as x increases. The graph always lies above the x-axis, but becomes arbitrarily close to it for large negative x; thus, the x-axis is a horizontal asymptote. The equation means that the slope of the tangent to the graph at each point is equal to its y-coordinate at that point.