Given the vector r(t)=cos⁡T,sin

Lawrence Dennis

Lawrence Dennis

Answered question

2022-08-18

Given the vector r(t)=cosT,sinT,ln(cosT) and point (1, 0, 0) find vectors T, N and B at that point.

Vector T is the unit tangent vector, so the derivative r(t) is needed.

Vector N is the normal unit vector, and the equation for it uses the derivative of T(t). 

The B vector is the binormal vector, which is a crossproduct of T and N.

Answer & Explanation

Eliza Beth13

Eliza Beth13

Skilled2023-05-31Added 130 answers

To find the vectors T, N, and B at the point (1, 0, 0) for the given vector function r(t)=cos(t),sin(t),ln(cos(t)), we need to calculate the derivatives and perform some vector operations.
First, let's find the unit tangent vector T. The unit tangent vector is the derivative of r(t), normalized to have a magnitude of 1:
T(t)=dr/dtdr/dt
Taking the derivative of r(t), we have:
r(t)=(sin(t),cos(t),sin(t)cos(t))
Simplifying, we get:
r(t)=(sin(t),cos(t),tan(t))
To find T(t), we need to normalize r'(t):
T(t)=r(t)r(t)
Calculating the magnitude of r'(t):
r(t)=sin2(t)+cos2(t)+tan2(t)
Simplifying further:
r(t)=1+tan2(t)=sec2(t)=sec(t)
Now, we can find T(t):
T(t)=(sin(t)sec(t),cos(t)sec(t),tan(t)sec(t))
Simplifying, we have:
T(t)=(sin(t)cos(t),cos2(t),sin(t))
To find the normal unit vector N, we differentiate T(t) with respect to t:
N(t)=dT/dtdT/dt
Differentiating T(t), we have:
dTdt=(cos2(t),2sin(t)cos(t),cos(t))
Calculating the magnitude of dT/dt:
dT/dt=cos4(t)+4sin2(t)cos2(t)+cos2(t)
Simplifying:
dT/dt=cos2(t)(cos2(t)+4sin2(t)+1)=cos2(t)(cos2(t)+sin2(t)+1)
Since cos2(t)+sin2(t)=1, we can further simplify:
dT/dt=cos2(t)·2=2cos(t)
Now, we can find N(t):
N(t)=(cos2(t)2cos(t),2sin(t)cos(t)2cos(t),cos(t)2cos(t))
Simplifying, we have:
N(t)=(cos(t)2,2sin(t)2,cos(t)2)
Simplifying further:
N(t)=(cos(t)2,sin(t),cos(t)2)
Finally, to find the binormal vector B, we can take the cross product of T(t) and N(t):
B(t)=T(t)×N(t)
Calculating the cross product, we have:
B(t)=((2cos(t)sin(t))/2,(cos2(t))/2(cos2(t))/2,(sin(t))/2(sin(t))/2)
Simplifying, we get:
B(t)=(cos(t)sin(t),0,sin(t))
Now, we can evaluate these vectors at the point (1, 0, 0) by substituting t=0 into the expressions for T(t), N(t), and B(t):
T=(sin(0)cos(0),cos2(0),sin(0))=(0,1,0)
N=(cos(0)2,sin(0),cos(0)2})=(12,0,12)
B=(cos(0)sin(0),0,sin(0))=(0,0,0)
Therefore, at the point (1, 0, 0), the vectors T, N, and B are (0, 1, 0), (12,0,12), and (0, 0, 0), respectively.

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