Calculating Speed of Geometric Progression - Mechanics

[LagrangeEuler]

One question. In the text

http://locomat.loria.fr/napier/napier1619construction.pdf

author calculate

$y′_β=−10^7a^t lna$
for
$y_β=10^7a^t$
(see pages 4 and 5)
why minus sign in derivative? $y_{\beta}'$ is speed. And they use minus sign as I see just to obtain positive quantity for $y′_β=10^7a^t lna$. Is there any relation between that sign and motion of the particle? Particle moves in the some law of geometric progression.

 

[jtbell]

http://locomat.loria.fr/napier/napie...nstruction.pdf

This link is not complete. It gives me a "Not Found" error in my Web browser. Could you please post a correct version of it?

 

[LagrangeEuler]

Try now.