Warning: these puzzles are so advanced, they'll make you question the very fabric of reality.
You have a circle with a radius of r. You place a loop within this circle, also with a radius of r. If the loop is perfectly concentric, what is the area of the smaller circle?
You have a function f(x) that is equal to f(f(x)). If f(x) = x^2 + 1, what is f(5)?
See more recursive puzzles and learn about the dangers of recursive thinking
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