Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Applications of Derivatives

Question:

The normal to the curve $x=a(1+\cos \theta)$, $y=a \sin \theta$ at '$\theta$' always passes through the fixed point

Options:

(a, a)

(a, 0)

(0, a)

none of these

Correct Answer:

(a, 0)

Explanation:

We have,

$x=a(1+\cos \theta), y=a \sin \theta$

∴   $\frac{d y}{d x}=\frac{\frac{d y}{d \theta}}{\frac{d x}{d \theta}}=\frac{a \cos \theta}{-a \sin \theta}=-\cot \theta$

The equation of the normal at $(a(1+\cos \theta), a \sin \theta)$ is

$y-a \sin \theta=\tan \theta\{x-a(1+\cos \theta)\}$

$\Rightarrow x \sin \theta-y \cos \theta=a \sin \theta$

Clearly, it passes through (a, 0).