Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Applications of Derivatives

Question:

The rate of change of the area of a circular disc with respect to its circumference when radius is 3 is:

Options:

6 unit

3 unit

$6 \pi$ unit

$2 \pi$ unit

Correct Answer:

3 unit

Explanation:

The correct answer is Option (2) - 3 unit

circumference $C = 2πr$

area $a = πr^2$

$\frac{da}{dr}=2πr$

$\frac{dc}{dr}=2π⇒\frac{da}{dc}=r$

$\left.\frac{da}{dc}\right]_{r=3}=3$ unit