The area (A) of a circle is a function of its radius (r) and is given by the function A = f(r) = πr2. What is the domain of this function?

The domain is the set of values that can be put into a function, usually x values. but in this case r values. So you should be thinking, "What values is r allowed to be?"

So, since we are considering a circle, and the radius r is a distance on that circle, r cannot be a negative value or 0. No other limitations are given to the problem, so you can make the radius as big as you would like. So the domain is `0<r<oo or D:(0,oo).`

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Is there a word/phrase for "unperformant"?

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