Unit Tangent Vector
1. **State the problem:** Find the unit tangent vector to the curve $$\mathbf{r}(t) = k t \ln(t) \mathbf{\hat{k}} + 4 t^3 \mathbf{\hat{i}} - 2 t \mathbf{\hat{j}}$$ at $$t=2$$.
2. **Find the derivative \(\mathbf{r}'(t)\):**
- Derivative of \(k t \ln(t)\) with respect to \(t\):
$$\frac{d}{dt}[k t \ln(t)] = k \left(\ln(t) + 1\right)$$ by the product rule.
- Derivative of \(4 t^3\):
$$\frac{d}{dt}[4 t^3] = 12 t^2$$.
- Derivative of \(-2 t\):
$$\frac{d}{dt}[-2 t] = -2$$.
Thus,
$$\mathbf{r}'(t) = 12 t^2 \mathbf{\hat{i}} - 2 \mathbf{\hat{j}} + k (\ln(t)+1) \mathbf{\hat{k}}$$.
3. **Evaluate \(\mathbf{r}'(2)\):**
- \(12 \times 2^2 = 12 \times 4 = 48\)
- \(-2\) remains the same
- \(k (\ln(2)+1)\) stays symbolic, write as \(k (\ln(2)+1)\)
So,
$$\mathbf{r}'(2) = 48 \mathbf{\hat{i}} - 2 \mathbf{\hat{j}} + k (\ln(2)+1) \mathbf{\hat{k}}$$.
4. **Find the magnitude of \(\mathbf{r}'(2)\):**
$$\|\mathbf{r}'(2)\| = \sqrt{48^2 + (-2)^2 + \left(k (\ln(2)+1)\right)^2} = \sqrt{2304 + 4 + k^2 (\ln(2)+1)^2} = \sqrt{2308 + k^2 (\ln(2)+1)^2}$$.
5. **Find the unit tangent vector \(\mathbf{T}(2)\):**
$$\mathbf{T}(2) = \frac{\mathbf{r}'(2)}{\|\mathbf{r}'(2)\|} = \frac{48 \mathbf{\hat{i}} - 2 \mathbf{\hat{j}} + k (\ln(2)+1) \mathbf{\hat{k}}}{\sqrt{2308 + k^2 (\ln(2)+1)^2}}$$.
**Final answer:**
The unit tangent vector at \( t=2 \) is
$$\boxed{\mathbf{T}(2) = \frac{48 \mathbf{\hat{i}} - 2 \mathbf{\hat{j}} + k (\ln(2)+1) \mathbf{\hat{k}}}{\sqrt{2308 + k^2 (\ln(2)+1)^2}}}$$.