Best Answer

81.

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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Q: What number must you add t complete the square x2 plus 18x equals -13?

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4

square root -5 minus 14 or - square root -5 minus 14

x2 + 20x - 39 = 0: Add 61 giving: x2 + 20x + 100 = (x + 10)2

-17

The idea is to take half the linear part (12, in this case), then square it. The constant part must be equal to this result.

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square root -5 minus 14 or - square root -5 minus 14

The constant term - the part without a variable - must be equal to the square of one half the linear term - the number in front of the "x". That is, it must be (12/2)2 = 36.

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If: x^2 +18x = 29 Then completing the square: (x+9)^2 -81 = 29 or (x+9)^2 = 110

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