What is the formula for curvature in a plane curve?

[themadhatter1]

Homework Statement

show that the curvature of a plane curve is $$\kappa=|\frac{d\phi}{ds}|$$ where phi is the angle between T and i; that is, phi is the inclination of the tangent line.

Homework Equations

The Attempt at a Solution

I'm not sure how to start this one out.

Any ideas?

 

[HallsofIvy]

Well, what is your definition of curvature? (Some texts use the formula you give as the definition of curvature. Obviously your text does not but we need to know what definition it does use to say where you should start.)