# Intrinsic equation / curvature question...?

##
Prove if #|psi| # is small then #kappa approx (d^2y)/(dx^2) ( 1 - 3/2 tan^2 psi ) #

Prove if

##### 1 Answer

Jul 29, 2018

For

By Binomial Expansion :

Because:

#y' = tan psi#

Then:

#tan psi ~~psi " for " abspsi " << "1 color(blue)(implies) abs(y') " << " 1 " if " abspsi "<< "1#

So ignoring

# kappa ~~ y'' (1 - 3/2tan^2psi ) " for " abspsi " << "1#