# Unit tangent vector of r(t) = (e^t)(cos t ) i + (e^t)(sin t

1. Oct 30, 2016

1. The problem statement, all variables and given/known data
Find the unit tangent vector T(t) for vector valued function r(t) = (e^t)(cos t ) i + (e^t)(sin t ) j + (e^t) k

2. Relevant equations

3. The attempt at a solution
i gt stucked here ...
, the ans is [1/ sqrt (3) ] [ (cos t -sin t ) i + (sin t + cos t ) j +k)

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2. Oct 30, 2016

### PeroK

You got $r'(t)$ okay, but you didn't calculate its magnitude correctly. I would factor out the $e^t$ term first. Then you need to take more care with your algebra.

3. Oct 30, 2016

My ans is [1/ sqrt (2) ] [ (cos t -sin t ) i + (sin t + cos t ) j +k)
But not
[1/ sqrt (3) ] [ (cos t -sin t ) i + (sin t + cos t )
j +k)

Is the given ans wrong ?

4. Oct 30, 2016