Finding Curvature of Helix Given Parametric Equation

[LRP0790]

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

 

[Redbelly98]

I don't know, but your answer disagrees with the simple case where b=0.