Post-UTME Mathematics 2015 Objective — Question 2
Question 2 of 40 from the Post-UTME Screening (Post-UTME) Mathematics 2015 Objective paper, with the correct answer and a full explanation.
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The radius of a circle is increasing at the rate of 0.4 cm/s. Find the rate of increase in cm^2/s of the area, when the radius is 5cm.
- A. 40*pi
- B. 10*pi
- C. 5*pi
- D. 4*piCorrect
Explanation
A = pi*r^2, dA/dt = 2*pi*r*(dr/dt) = 2*pi*5*0.4 = 4*pi.
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