What is the unit tangent vector to r(t)=⟨cost,sint,0⟩\mathbf{r}(t) = \langle \cos t, \sin t, 0 \rangler(t)=⟨cost,sint,0⟩ at t=π/4t = \pi/4t=π/4?
⟨−22,22,0⟩\langle -\frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2}, 0 \rangle⟨−22,22,0⟩
⟨22,22,0⟩\langle \frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2}, 0 \rangle⟨22,22,0⟩
⟨0,1,0⟩\langle 0, 1, 0 \rangle⟨0,1,0⟩
⟨−1,0,0⟩\langle -1, 0, 0 \rangle⟨−1,0,0⟩