Yes, 21, 220, 221 can form a right triangle. To determine if a set of three numbers can form a right triangle, we can use the Pythagorean theorem, which states that in a right triangle, the square of the length of the hypotenuse (the longest side) is equal to the sum of the squares of the lengths of the other two sides. In this case, we have:
Since 221^2 is equal to the sum of the squares of 21 and 220, these three numbers form a Pythagorean triple and can form a right triangle..
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