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Rate of change of circle inside a square (difficult)

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Reply 20
Avatar for F1Addict
F1Addict
12
Original post by JonathanM
Urm what?
a76b64967e6a404185e953b.png

The question says a circle inside square, not a square inside circle. You mixed the two up, hence the confusion.
Reply 21
Avatar for JonathanM
JonathanM
2
Circle inside a square omg

Wow sorry for that it's good I drew a diagram.
Original post by JonathanM
Urm what?
a76b64967e6a404185e953b.png


Have you read the question?
Reply 23
Avatar for Tyraell
Tyraell
13
Original post by JonathanM
Circle inside a square omg

Wow sorry for that it's good I drew a diagram.


Awkwaaard
Reply 24
Avatar for JonathanM
JonathanM
2
Original post by steve2005
Have you read the question?


I did but I do this frequently. It's something I do a lot even though I believe I've read something and understand. I've done it in exams before. It's a stupid problem which shouldn't exist. Questions like this are easy and worth loads of marks.

Original post by hassi94
Wow I don't think you're getting this. It has absolute relevance.

If d/dt (2pi r) = 6 then d/dt (r) = 6/2pi = 3/pi

And you can logically work out that the square must be of side 2r and so the perimeter is 8r.

Then we can write d/dt(8r) = 24/pi


I don't ever work out connected rates of changes like this lol. I enjoy making chain rule apparent even though you just disguised it pretty much xD.

dP/dt = dP/dC*dC/dt
dC/dt = 6
Perimiter = 4x
Circumference = pi*x
P = 4(C/pi)
dP/dC = 4/pi
Therefore dP/dt = 24/pi

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