The problem asks to find the symmetric equations of the tangent line to the curve given by the vector function $\mathbf{r}(t) = 2\cos{t} \mathbf{i} + 6\sin{t} \mathbf{j} + t \mathbf{k}$ at $t = \pi/3$.

GeometryVector CalculusTangent LinesParametric EquationsSymmetric Equations3D Geometry
2025/4/13

1. Problem Description

The problem asks to find the symmetric equations of the tangent line to the curve given by the vector function r(t)=2costi+6sintj+tk\mathbf{r}(t) = 2\cos{t} \mathbf{i} + 6\sin{t} \mathbf{j} + t \mathbf{k} at t=π/3t = \pi/3.

2. Solution Steps

First, find the derivative of r(t)\mathbf{r}(t) with respect to tt:
r(t)=2sinti+6costj+k\mathbf{r}'(t) = -2\sin{t} \mathbf{i} + 6\cos{t} \mathbf{j} + \mathbf{k}
Next, evaluate r(t)\mathbf{r}'(t) at t=π/3t = \pi/3:
r(π/3)=2sin(π/3)i+6cos(π/3)j+k=2(3/2)i+6(1/2)j+k=3i+3j+k\mathbf{r}'(\pi/3) = -2\sin{(\pi/3)} \mathbf{i} + 6\cos{(\pi/3)} \mathbf{j} + \mathbf{k} = -2(\sqrt{3}/2) \mathbf{i} + 6(1/2) \mathbf{j} + \mathbf{k} = -\sqrt{3} \mathbf{i} + 3 \mathbf{j} + \mathbf{k}
This vector r(π/3)=3,3,1\mathbf{r}'(\pi/3) = \langle -\sqrt{3}, 3, 1 \rangle gives the direction vector of the tangent line.
Now, evaluate r(t)\mathbf{r}(t) at t=π/3t = \pi/3:
r(π/3)=2cos(π/3)i+6sin(π/3)j+(π/3)k=2(1/2)i+6(3/2)j+(π/3)k=i+33j+(π/3)k\mathbf{r}(\pi/3) = 2\cos{(\pi/3)} \mathbf{i} + 6\sin{(\pi/3)} \mathbf{j} + (\pi/3) \mathbf{k} = 2(1/2) \mathbf{i} + 6(\sqrt{3}/2) \mathbf{j} + (\pi/3) \mathbf{k} = \mathbf{i} + 3\sqrt{3} \mathbf{j} + (\pi/3) \mathbf{k}
So the point on the curve at t=π/3t = \pi/3 is (1,33,π/3)(1, 3\sqrt{3}, \pi/3).
The parametric equations of the tangent line are:
x=13tx = 1 - \sqrt{3}t
y=33+3ty = 3\sqrt{3} + 3t
z=π/3+tz = \pi/3 + t
To find the symmetric equations, solve for tt in each equation:
t=1x3t = \frac{1-x}{\sqrt{3}}
t=y333t = \frac{y - 3\sqrt{3}}{3}
t=zπ3t = z - \frac{\pi}{3}
Now, set these expressions for tt equal to each other:
1x3=y333=zπ3\frac{1-x}{\sqrt{3}} = \frac{y - 3\sqrt{3}}{3} = z - \frac{\pi}{3}

3. Final Answer

The symmetric equations of the tangent line are:
1x3=y333=zπ3\frac{1-x}{\sqrt{3}} = \frac{y - 3\sqrt{3}}{3} = z - \frac{\pi}{3}

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