What polynomial identity should be used to prove that 252 = (20 5)2?

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What polynomial identity should be used to prove that 252 = (20 5)2?

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25² = (20 + 5) ² Here is a binocular:
(a + b) ² = a² + 2 ab + b²
625 = 20² + 2 · 20 · 5 + 5²
625 = 400 + 200 + 25
625 = 625 (correct)