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Question from an exam that I need help with...

Not sure which exam it is off, but I am looking for help on this question, really unsure. It was apparently on the Higher Calculator paper, god knows what year, sorry, because my teacher only printed the question off. Anyhow, it looks like this...

A circle has an area of 100m2.
Work out the circumference of the circle.
Give your answer correct to 3 significant figures.

There's no diameter or radius, or anything, just a circle drawn. I was trying to find out the diameter of the circle by dividing the area by Pi (3.142) and then square rooting the answer, to give me a diameter, not sure whether that's right? Not sure if it's a hard question, but I found some harder questions easier. Hmm. I'd appreciate some help, tomorrow's the exam, and it would be helpful to know, just in case something like that does come up.
You know πr2=100\pi r^2 = 100

Use this to work out radius (NOT diameter) the way you said.

Then double to get diameter.

Then find circumference as normal.
Reply 2
Alright, cool, didn't come across that formula, thanks. So to clarify, what you mean is by dividing the 100 by the Pi, you get the radius squared, is that right? Then square root it and double to get the diameter?
Original post by Kamil95
Alright, cool, didn't come across that formula, thanks. So to clarify, what you mean is by dividing the 100 by the Pi, you get the radius squared, is that right? Then square root it and double to get the diameter?


yes
Reply 4
What you have done is correct (100/pi = r) but it would give you the radius, not the diameter. And then just do (2 pi r) and there is your circumference :smile:
Reply 5
Hmm, actually it doesn't sound that hard once you know it. Thanks for helping me out :smile:

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