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I have been asked to find the rate of change of the area of a square with respect to the length of its side when the side is 4ft.

This is how I thought I should do it.

Area=$s^2$

$\frac{d(a)}{d(s)}=2 s$

Now I thought that I could just replace s with 4ft, however the answer is $\frac{8 \text{ft}^2}{\text{ft}}$,

what am I missing?

Gerry Myerson
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ALEXANDER
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1 Answers1

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$8 ft^2/ft = 8 ft$, which is the answer your formula gives. So your work appears to be correct.

PepeOfMath
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    But writing it as 8 square feet per foot emphasizes that it's the rate of change of an area with respect to a length. – Gerry Myerson Aug 02 '14 at 07:56
  • Thats okey but it is not only this question where de represent the answer in this way, I just dont understand why? Why not simplify? – ALEXANDER Aug 02 '14 at 19:14
  • Okey thats why they do it, sorry didnt update the browser before I asked the question! – ALEXANDER Aug 02 '14 at 19:15