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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: 1 month ago
Views: 10
1 month 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
1706 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
1 month ago
Sorry, dr/dt = 1/12 cm/s. Correction.