The eccentric angle of the point $\mathrm{P}(-6,2)$ of the ellipse $\frac{x^2}{48}+\frac{y^2}{16}=1$ is
- $30^{\circ}$
- $135^{\circ}$
- $150^{\circ}$
- $120^{\circ}$
Solution
The ellipse is defined by the equation $\frac{x^2}{48}+\frac{y^2}{16}=1$.
By comparing with the standard form $\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$, we find $a=4\sqrt{3}$ and $b=4$.
The parametric coordinates of any point on the ellipse are given by $(a\cos\theta, b\sin\theta)$, where $\theta$ is the eccentric angle.
For the point $\mathrm{P}(-6,2)$, we set:
$4\sqrt{3}\cos\theta = -6$ and $4\sin\theta = 2$.
Solving the second equation gives $\sin\theta = \frac{1}{2}$.
From the first equation, $\cos\theta = \frac{-6}{4\sqrt{3}} = -\frac{\sqrt{3}}{2}$ after rationalization.
Given that $\sin\theta$ is positive and $\cos\theta$ is negative, $\theta$ must lie in the second quadrant.
The reference angle where $\sin\alpha = \frac{1}{2}$ and $\cos\alpha = \frac{\sqrt{3}}{2}$ is $30^{\circ}$.
Thus, $\theta = 180^{\circ} - 30^{\circ} = 150^{\circ}$.
$\boxed{150^{\circ}}$
~Asked in: MHT CET 2025 (05 May Shift 2)