Question 630633: Solve by completing the square what value should you add to each side of the equation x^2+18x=-9 Found 2 solutions by stanbon, Edwin McCravy:Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website! Solve by completing the square what value should you add to each side of the equation x^2+18x=-9
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x^2 + 18x + (18/2)^2 = -9 + (18/2)^2
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Answer: (18/2)^2 = 9^2 = 81
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Cheers,
Stan H.
x² + 18x = -9
Rule for finding the number to add to both sides to complete the square:
1. Multiply the coefficient of x by
2. Square the result of step 1.
The coefficient of x is 18
1. 18· = 9
2. 9² = 81
So we must add 81 to both sides
That's all you were asked for.
To solve the equation,
x² + 18x = -9
add 81 to both sides:
x² + 18x + 81 = -9 + 81
Factor the left side
(x + 9)(x + 9) = 72
Write the left side as the square of a binomial:
(x + 9)² = 72
Use the principle of square roots.
1. Eliminate the square and the parentheses on the left.
2. Take ± the square roots of the right side:
x + 9 =
x + 9 =
x + 9 =
x = -9 ± 6
Two solutions:
x = -9 + 6 and x = -9 - 6
Edwin
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