# Curvature of a Helix

## Homework Statement

Find the curvature of a helix given by the parametric equation r(t)=<acost, asint, bt> where a and b are real numbers

## Homework Equations

I know k=|T'(t)/r'(t)|

## The Attempt at a Solution

and I believe the answer to be k=b/(a2+b2)1/2, I just don't know how to get there

HallsofIvy
If so then if r= <a cos t, a sin t, bt>, r'= <-a sin t, a cos t, b> and it's length is $|r'|= \sqrt{a^2 sin^2 t+ a^2 sin^2 t+ b^2}= \sqrt{a^2+ b^2}$, a constant. That means that T, the unit tangent vector is
$$T= \frac{1}{\sqrt{a^2+ b^2}}<-a sin t, a cos t, b>$$