In calculus, the primary significance of 1/x is its value as the derivative of the natural logarithm of "x." The proof for the derivative of ln(x) may be found by defining the inverse of the natural logarithm, expressed as e^y = x.
The derivative of a function is used to find the slope of the tangent at a given value of "x." Finding the derivative of both sides in respect to "x" gives the equation e^y dy/dx = 1, as the derivative of "x" is 1. Because e^y is equal to "x," then x dy/dx = 1, and dividing both sides of the equation by "x" gives the proof that d/dx of ln(x) = 1/x.