q

[reef nest]

Also, when I said “because u and lnx are both one-to-one”, I think what I meant to say is that the substitution is one-to-one (if that makes sense)?

[twilit umbra]

Well $u=\ln(x)$, if you have learnt logarithm function or derivatives you know that $y=\ln(x)$ is increasing so $x \uparrow \Rightarrow u=\ln(x) \uparrow$

[obtuse vector]

Alexis_Fx

[twilit umbra]

That means if x reach its minimum so do $u=\ln(x)$

[obtuse vector]

Alexis_Fx