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Principal unit normal vector for $$$\mathbf{\vec{r}\left(t\right)} = \left\langle e^{t} \cos{\left(t \right)}, e^{t} \sin{\left(t \right)}, e^{t}\right\rangle$$$
Related calculators: Unit Tangent Vector Calculator, Unit Binormal Vector Calculator
Your Input
Find the principal unit normal vector for $$$\mathbf{\vec{r}\left(t\right)} = \left\langle e^{t} \cos{\left(t \right)}, e^{t} \sin{\left(t \right)}, e^{t}\right\rangle$$$.
Solution
To find the principal unit normal vector, we need to find the derivative of the unit tangent vector $$$\mathbf{\vec{T}\left(t\right)}$$$ and then normalize it (find the unit vector).
Find the unit tangent vector: $$$\mathbf{\vec{T}\left(t\right)} = \left\langle \frac{\sqrt{6} \cos{\left(t + \frac{\pi}{4} \right)}}{3}, \frac{\sqrt{6} \sin{\left(t + \frac{\pi}{4} \right)}}{3}, \frac{\sqrt{3}}{3}\right\rangle$$$ (for steps, see unit tangent vector calculator).
$$$\mathbf{\vec{T}^{\prime}\left(t\right)} = \left\langle - \frac{\sqrt{6} \sin{\left(t + \frac{\pi}{4} \right)}}{3}, \frac{\sqrt{6} \cos{\left(t + \frac{\pi}{4} \right)}}{3}, 0\right\rangle$$$ (for steps, see derivative calculator).
Find the unit vector: $$$\mathbf{\vec{N}\left(t\right)} = \left\langle - \sin{\left(t + \frac{\pi}{4} \right)}, \cos{\left(t + \frac{\pi}{4} \right)}, 0\right\rangle$$$ (for steps, see unit vector calculator).
Answer
The principal unit normal vector is $$$\mathbf{\vec{N}\left(t\right)} = \left\langle - \sin{\left(t + \frac{\pi}{4} \right)}, \cos{\left(t + \frac{\pi}{4} \right)}, 0\right\rangle$$$A.