Square root estimate
Definition · Level 13 · Interview mechanics
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√x ≈ a + (x − a²) ÷ 2a, with a the nearest easy root. The error is tiny when x is close to a².
Example
√130: 11² = 121, so ≈ 11 + 9/22 = 11.41 (exact 11.40).
Where Tradecraft teaches it
Level 13 · Interview mechanics, in the lesson “Compounding, roots and annualizing volatility”: Doubling time, compound growth, square roots, volatility between days and years, and basis points.
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