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Question: The equation of the tangent to the circle, given by $x = 5 \cos \theta, y = 5 \sin \theta$ at the po...

The equation of the tangent to the circle, given by x=5cosθ,y=5sinθx = 5 \cos \theta, y = 5 \sin \theta at the point θ=π3\theta = \frac{\pi}{3} on it, is

A

x3y=5x - \sqrt{3}y = -5

B

x+3y=10x + \sqrt{3}y = 10

C

3x+y=53\sqrt{3}x + y = 5\sqrt{3}

D

3xy=0\sqrt{3}x - y = 0

Answer

x + √3y = 10

Explanation

Solution

For a circle with parametric equations

x=5cosθ,y=5sinθx = 5\cos\theta, y = 5\sin\theta,

the equation of the tangent at the point corresponding to θ\theta is given by:

xcosθ+ysinθ=5x\cos\theta + y\sin\theta = 5.

At θ=π3\theta = \frac{\pi}{3}, we have:

cosπ3=12,sinπ3=32\cos\frac{\pi}{3} = \frac{1}{2}, \sin\frac{\pi}{3} = \frac{\sqrt{3}}{2}.

Substitute these into the tangent equation:

x(12)+y(32)=5x\left(\frac{1}{2}\right) + y\left(\frac{\sqrt{3}}{2}\right) = 5.

Multiply through by 2 to eliminate fractions:

x+3y=10x + \sqrt{3} y = 10.

This corresponds to Option B.