I'm struggling to find the method to use when trying to get the normal vector(adsbygoogle = window.adsbygoogle || []).push({}); nto a (flat) surface at a specific point. Every textbook I've researched has the same scenerio, where they show how to get aplanegiven a point and normal vector, but I have the opposite problem, where I know the plane and know the point but want thenormal. And since that method uses a dot product I can't simply "undo" it to findn.

I know how to get the general normal to the surface by taking the gradient of the plane equation, but I need the specific one that goes through a known coordinate.

And sorry to make it more difficult, but this is in cylindrical coordinates... if there is a way to do this without converting to Cartesian that would be some excellent information.

Thanks

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Analytic Geometry - finding the normal vector at a point

**Physics Forums | Science Articles, Homework Help, Discussion**