# Unit Normal Vector to non-parametrized curve

• Feb 25th 2009, 05:29 AM
newprint
Unit Normal Vector to non-parametrized curve
I got a curve, that is non parametrized and I need to find principal unit normal vector to that curve at certain point

in my case it is y=e^x at point x=1

what do I do ??
• Feb 25th 2009, 05:58 AM
Abu-Khalil
In $\displaystyle \mathbb{R}^2$ or $\displaystyle \mathbb{R}^3$?

Anyway, if you derivate you'll get $\displaystyle \frac{dy}{dx}=e^x$, so the tangent line in $\displaystyle x=1$ has a slope equal to $\displaystyle e$, therefore the normal line to the curve in that point has a slope $\displaystyle -\frac{1}{e}$. Let $\displaystyle \vec{n}=\left(1,-\frac{1}{e}\right)$ then your vector is $\displaystyle \hat{n}=\frac{\vec{n}}{||\vec{n}||}$.
• Feb 25th 2009, 07:09 AM
HallsofIvy
It's actually unusual for a curve in two dimensions as parametric equations since it is simpler to write it as a single xy equation. If that was a problem and you knew how to find a normal vector for a parameterized curve, let x itself be the parameter: x= t, y= $\displaystyle e^t$.