How many circles have an area of 36 pi meters squared?

Well, the area of a circle = 
so 36 pi = r^2 pi

the pi's cancel and you're left with 36 = r^2

square root both sides to get  = r
and r = + or - 6

However, a circle cannot have a negative radius so r = 6 and only a circle with a radius of 6 has an area of 36 pi

To answer your question briefly, there is one circle with an area of 36 pi

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