For a tiny bit more math-y information: pi relates the diameter and the circumference of a circle by the definition of pi!
I can also break down the calculus to find the are equation if anyone actually wants to see it, as calculus practice or just for fun 
Cool handwriting
This reminds me that I need to study 
Back to basics!
I really need this for revision. 
I used to really enjoy this in Maths class! And this is a great summary of the basics for circles. I always forgot C and A equations
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