- #1

chetzread

- 801

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## Homework Statement

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find the curvature of the vector valued function r(t) = 3sint i + 3cost j +4t k

## Homework Equations

## The Attempt at a Solution

For the unit tangent vector , i got T(t) = (3cost i -3sint j +4k) / sqrt (9 ((sint)^2 ) + 9 ((cost)^2 ) + 4^2 ) =

(3cost i -3sint j +4k) / 5

For the principal unit vector , N(t) , i got -3sint i -3cost j ) / sqrt (9 ((sint)^2 ) + 9 ((cost)^2 )

= -sint i -cost j

We can conclude that |r'(t) | = 5 , |T'(t) | = 3 , so , curvature = |T'(t) | / |r'(t) | = 3/5 , but the ans is 3/25 , which part of my working is wrong ?

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