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

GeometryVector CalculusTangent LinesParametric EquationsSymmetric Equations3D Geometry
2025/6/3

1. Problem Description

The problem asks to find the symmetric equations of the tangent line to the curve defined by the vector function r(t)=2cos(t)i^+6sin(t)j^+tk^\vec{r}(t) = 2 \cos(t) \hat{i} + 6 \sin(t) \hat{j} + t \hat{k} at t=π3t = \frac{\pi}{3}.

2. Solution Steps

First, we need to find the derivative of r(t)\vec{r}(t) with respect to tt, which represents the tangent vector to the curve.
r(t)=ddt(2cos(t)i^+6sin(t)j^+tk^)\vec{r}'(t) = \frac{d}{dt}(2 \cos(t) \hat{i} + 6 \sin(t) \hat{j} + t \hat{k})
r(t)=2sin(t)i^+6cos(t)j^+1k^\vec{r}'(t) = -2 \sin(t) \hat{i} + 6 \cos(t) \hat{j} + 1 \hat{k}
Next, we evaluate the tangent vector at t=π3t = \frac{\pi}{3}:
r(π3)=2sin(π3)i^+6cos(π3)j^+1k^\vec{r}'(\frac{\pi}{3}) = -2 \sin(\frac{\pi}{3}) \hat{i} + 6 \cos(\frac{\pi}{3}) \hat{j} + 1 \hat{k}
Since sin(π3)=32\sin(\frac{\pi}{3}) = \frac{\sqrt{3}}{2} and cos(π3)=12\cos(\frac{\pi}{3}) = \frac{1}{2},
r(π3)=2(32)i^+6(12)j^+1k^\vec{r}'(\frac{\pi}{3}) = -2(\frac{\sqrt{3}}{2}) \hat{i} + 6(\frac{1}{2}) \hat{j} + 1 \hat{k}
r(π3)=3i^+3j^+1k^\vec{r}'(\frac{\pi}{3}) = -\sqrt{3} \hat{i} + 3 \hat{j} + 1 \hat{k}
Now, we need to find the position vector r(π3)\vec{r}(\frac{\pi}{3}):
r(π3)=2cos(π3)i^+6sin(π3)j^+π3k^\vec{r}(\frac{\pi}{3}) = 2 \cos(\frac{\pi}{3}) \hat{i} + 6 \sin(\frac{\pi}{3}) \hat{j} + \frac{\pi}{3} \hat{k}
r(π3)=2(12)i^+6(32)j^+π3k^\vec{r}(\frac{\pi}{3}) = 2(\frac{1}{2}) \hat{i} + 6(\frac{\sqrt{3}}{2}) \hat{j} + \frac{\pi}{3} \hat{k}
r(π3)=1i^+33j^+π3k^\vec{r}(\frac{\pi}{3}) = 1 \hat{i} + 3\sqrt{3} \hat{j} + \frac{\pi}{3} \hat{k}
Thus, the point on the curve is (1,33,π3)(1, 3\sqrt{3}, \frac{\pi}{3}).
The tangent line has the direction vector r(π3)=<3,3,1>\vec{r}'(\frac{\pi}{3}) = <-\sqrt{3}, 3, 1>. The parametric equations of the tangent line are given by:
x=13tx = 1 - \sqrt{3}t
y=33+3ty = 3\sqrt{3} + 3t
z=π3+tz = \frac{\pi}{3} + t
To find the symmetric equations, we solve for tt in each equation:
t=x13t = \frac{x - 1}{-\sqrt{3}}
t=y333t = \frac{y - 3\sqrt{3}}{3}
t=zπ3t = z - \frac{\pi}{3}
Therefore, the symmetric equations are:
x13=y333=zπ3\frac{x - 1}{-\sqrt{3}} = \frac{y - 3\sqrt{3}}{3} = z - \frac{\pi}{3}

3. Final Answer

x13=y333=zπ3\frac{x-1}{-\sqrt{3}} = \frac{y-3\sqrt{3}}{3} = z-\frac{\pi}{3}

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