Derivative of x^n by Bessel Function of the First Kind of Order n of x

Theorem
Let $\map {J_n} x$ denote the Bessel function of the first kind of order $n$.

Then:
 * $\map {\dfrac \d {\d x} } {x^n \map {J_n} x} = x^n \map {J_{n - 1} } x$