Ang Yew Keong's answer to Christine Goh's Secondary 4 A Maths question.

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Ang Yew Keong
Ang Yew Keong's answer
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Tan Wee Leng
Tan Wee Leng
2 years ago
Final answer on the rate of change of perimeter is incorrect.

The working on finding the rate of change of x is done correctly.
However, the perimeter being a function of x is not considered.

Perimeter is 10x,
dP/dt = (dP/dx)*(dx/dt)
= (10)*(1cm/s) = 10cm/s

(the units for dA/dx found in this answer should be cm instead)