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secondary 4 | A Maths
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Georgia Jansen
Georgia Jansen

secondary 4 chevron_right A Maths chevron_right Singapore

Ans is 1/12 but I got 16(pie)r

Date Posted: 4 months ago
Views: 15
4 months ago
dA/dt = 8cm²/s

Area of circle, A = πr²
dA/dr = 2πr

dr/dt = dA/dt x dr/dA

= dA/dt ÷ dA/dr

= 8 ÷ 2πr

Since circumference = 96cm and we know that circumference = 2πr,

dr/dt = 8cm²/s ÷ 96cm = 1/12 cm/s

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Eric Nicholas K
Eric Nicholas K's answer
2980 answers (Tutor Details)
We are given the circumference of the circle. We must extract the radius out of this data.

Subsequently, we define the area of the circle and then evaluate dA/dr when r = the radius which you obtained earlier.

You are also given that dA/dt.

By the chain rule,

dA/dt = dA/dr * dr/dt

Sub in values of dA/dt and dA/dr.
Eric Nicholas K
Eric Nicholas K
4 months ago
Sorry, dr/dt = 1/12 cm/s. Correction.