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공식x = [-b ± √(b^2 - 4ac)]/2a증명$$ a x² + b x + c = 0 $$$$ x² + (b/a) x + (c/a) = 0 $$$$ [x² + 2*(b/2a) x + (b/2a)²] + (c/a) = (b/2a)² $$$$ [x + b/2a]² = [(b²/4a²) - (c/a)] = (b² - 4ac)/4a² $$$$ x + b/2a = ± √(b² — 4 a c)/2 a $$$$ x = ± √(b² — 4 a c)/2 a - b/2a $$$$ x = [-b ± √(b^2 — 4 a c)] / 2 a $$