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Principal unit normal vectors: Find the principal unit normal vector for the given function at the specified value of t.

r(t)=sint,cost, where and are positive,t=0

Short Answer

Expert verified

Ans: The principal unit normal vector of r(t)=sint,costat t=0is0,-1

Step by step solution

01

Step 1. Given information:

r(t)=sint,cost, where and are positive, t=0

02

Step 2. Simplifying the principal unit normal vector:

The principal unit normal vector of r(t)denoted by N(t)is given by

N(t)=T'(t)T'(t)where T(t)=r'(t)r'(t)

T(t)should be calculated first and then N(t)is to be evaluated.

We start by comparing r'(t)first:

r'(t)=cost,-sintr'(t)=(cost)2+(-sint)2=22cos2t+sin2t=

The unit tangent vector

T(t)=r'(t)r'(t)=cost,-sint=cost,-sint

To find N(t)we divide T'(t)by its magnitude.

T'(t)=-sint,-costT'(t)=(-sint)2+(-cost)2=2sin2t+cos2t=

03

Step 3. Finding the principal unit normal vector:

The principal unit normal vector

N(t)=T'(t)T'(t)=-sint,-cost=-sint,-cost

At t=0,N(t)=N(0)=-sin0,-cos0=0,-1

Thus the principle unit normal vector of r(t)at t=0is 0,-1

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