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ID:
Class: 12
Subject: Math
Topic: Application of Derivative
Type: Mcq
Question:
The rate of change of the area of a circle with respect to its radius \(r\) at \(r = 6\;{\text{cm}}\) is
A.
10\(\pi\)
B.
12\(\pi\)
C.
8\(\pi\)
D.
11\(\pi\)
Official Solution
Correct Answer:
12\(\pi\)
Explanation:
The rate of change of the area of a circle with respect to its radius \(r\) at \(r = 6,\text{cm}\) is to be determined.\[\]
We know that the area of a circle is:
\(A = \pi r^2\)
Differentiate with respect to \(r\):
\[\dfrac{dA}{dr} = \dfrac{d}{dr}(\pi r^2) = 2\pi r\]
Now, substitute \(r = 6\):
\[\dfrac{dA}{dr} = 2\pi \cdot 6 = 12\pi,\text{cm}^2/\text{cm}\]
Final Answer:
The rate of change of the area at \(r = 6,\text{cm}\) is \(12\pi,\text{cm}^2/\text{cm}\).
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