Math Problem Statement

Find a parametrization of the tangent line to r(t) = (ln(t))i + t^-1j + 11tk at the point t = 1.

Solution

To find a parametrization of the tangent line to the vector-valued function r(t)=(ln(t))i+t1j+11tk\mathbf{r}(t) = (\ln(t))\mathbf{i} + t^{-1}\mathbf{j} + 11t\mathbf{k} at the point t=1t = 1, let's proceed with these steps:

Step 1: Calculate the Derivative r(t)\mathbf{r}'(t)

To determine the tangent line, we first need the derivative r(t)\mathbf{r}'(t), which represents the velocity vector.

r(t)=ln(t),t1,11t\mathbf{r}(t) = \langle \ln(t), t^{-1}, 11t \rangle

Now, differentiate each component with respect to tt:

  1. x(t)=ln(t)x(t) = \ln(t)
    x(t)=1tx'(t) = \frac{1}{t}

  2. y(t)=t1y(t) = t^{-1}
    y(t)=t2y'(t) = -t^{-2}

  3. z(t)=11tz(t) = 11t
    z(t)=11z'(t) = 11

Thus, the derivative vector is:

r(t)=1t,t2,11\mathbf{r}'(t) = \left\langle \frac{1}{t}, -t^{-2}, 11 \right\rangle

Step 2: Evaluate the Derivative at t=1t = 1

To find the direction of the tangent line at t=1t = 1, substitute t=1t = 1 into r(t)\mathbf{r}'(t):

r(1)=11,12,11=1,1,11\mathbf{r}'(1) = \left\langle \frac{1}{1}, -1^{-2}, 11 \right\rangle = \langle 1, -1, 11 \rangle

Step 3: Find the Point r(1)\mathbf{r}(1)

We also need the position vector at t=1t = 1:

r(1)=ln(1),11,11×1=0,1,11\mathbf{r}(1) = \langle \ln(1), 1^{-1}, 11 \times 1 \rangle = \langle 0, 1, 11 \rangle

Step 4: Parametrize the Tangent Line

The parametrization of the tangent line L(t)\mathbf{L}(t) can be given by:

L(t)=r(1)+tr(1)\mathbf{L}(t) = \mathbf{r}(1) + t \mathbf{r}'(1)

Substituting the values we have:

L(t)=0,1,11+t1,1,11\mathbf{L}(t) = \langle 0, 1, 11 \rangle + t \langle 1, -1, 11 \rangle

Expanding this gives:

L(t)=0+t1,1+t(1),11+t11\mathbf{L}(t) = \langle 0 + t \cdot 1, 1 + t \cdot (-1), 11 + t \cdot 11 \rangle

L(t)=t,1t,11+11t\mathbf{L}(t) = \langle t, 1 - t, 11 + 11t \rangle

Final Answer

L(t)=t,1t,11+11t\mathbf{L}(t) = \langle t, 1 - t, 11 + 11t \rangle

Would you like further clarification on any part of the process? Here are some related questions to consider:

  1. How do you find the derivative of a vector-valued function?
  2. Why do we use the derivative to find the tangent line?
  3. How do you parametrize lines in three-dimensional space?
  4. Can we extend this method to curves in higher dimensions?
  5. What is the geometric significance of the tangent vector at a given point?

Tip: When finding the tangent line to a curve, always evaluate both the position vector and the derivative at the point of interest to obtain the correct line parametrization.

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Math Problem Analysis

Mathematical Concepts

Vector-valued functions
Parametrization
Tangent lines
Calculus

Formulas

r'(t) = derivative of r(t)

Theorems

Derivative of vector-valued functions
Tangent line theorem

Suitable Grade Level

University level (Calculus II or III)