How did the author compute highlighted term 2 from the highlighted term 1 in the following answer to the given question?
If $\rho =\frac{d\psi}{ds}$, then term 2 should be $\upsilon^2\frac{d\hat{T}}{d\psi}\rho$ but instead it was written $\frac{\upsilon^2}{\rho}\frac{d\hat{T}}{d\psi}$
How is that computed ? How to compute radius of curvature?
$note=\frac{d\hat{T}}{ds}=\kappa\hat{N}$
