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An equilateral triangle's sides increase...

An equilateral triangle's sides increase at the rate of 2cm/sec. If the area of its incircle increases at a rate of `kcm^(2)//sec` (when the length of the side is `(6)/(pi)cm`), then the value of k is

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To solve the problem, we need to find the rate of increase of the area of the incircle of an equilateral triangle when the side length is \( \frac{6}{\pi} \) cm and the sides of the triangle are increasing at a rate of 2 cm/sec. ### Step-by-Step Solution: 1. **Identify the Variables**: - Let \( x \) be the length of a side of the equilateral triangle. - The radius \( r \) of the incircle can be expressed in terms of \( x \). 2. **Find the Radius of the Incircle**: - For an equilateral triangle, the radius \( r \) of the incircle is given by: \[ r = \frac{x \sqrt{3}}{6} \] 3. **Find the Area of the Incircle**: - The area \( A \) of the incircle is given by: \[ A = \pi r^2 = \pi \left(\frac{x \sqrt{3}}{6}\right)^2 = \pi \frac{3x^2}{36} = \frac{\pi x^2}{12} \] 4. **Differentiate the Area with Respect to Time**: - To find the rate of change of the area with respect to time, differentiate \( A \): \[ \frac{dA}{dt} = \frac{d}{dt}\left(\frac{\pi x^2}{12}\right) = \frac{\pi}{12} \cdot 2x \frac{dx}{dt} = \frac{\pi x}{6} \frac{dx}{dt} \] 5. **Substitute Known Values**: - We know that \( \frac{dx}{dt} = 2 \) cm/sec and we need to evaluate this when \( x = \frac{6}{\pi} \): \[ \frac{dA}{dt} = \frac{\pi \left(\frac{6}{\pi}\right)}{6} \cdot 2 = \frac{6}{6} \cdot 2 = 2 \text{ cm}^2/\text{sec} \] 6. **Conclusion**: - Since we are given that the area of the incircle increases at a rate of \( k \) cm²/sec, we find that: \[ k = 2 \] ### Final Answer: The value of \( k \) is \( 2 \).
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Knowledge Check

  • The sides of an equilateral triangle are increasing at the rate of 2 cm/sec . The rate of which its area increases, when side is 10 cm, is

    A
    `10 cm^(2) // sec`
    B
    `10 sqrt(3) cm^(2) // sec `
    C
    ` (10)/( 3) cm^(2) // sec`
    D
    `sqrt( 3) cm^(2) // sec`
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