Why the derivative of ln(ax) is 1/x
Chain rule: d/dx[ln(ax)] = (1 / ax) · a = 1/x. The a cancels.
Log rule: ln(ax) = ln(a) + ln(x). ln(a) is a constant with derivative 0, leaving d/dx[ln(x)] = 1/x.
The function ln(ax) is only defined where ax > 0, so for a > 0 you need x > 0.


