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To complete the square, halve the coefficient of the x term (18/2 = 9) and add the square of this (92 = 81) to both sides:

x2 + 18x = -13

⇒ x2 + 18x + 81 = -13 + 81

⇒ (x + 9)2 = 68

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2011-08-31 09:40:15
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Q: What number must you add t complete the square x2 plus 18x equals -13?
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