What number would you add to the equation below to complete the square? x2 + 4x = 0?

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Equation
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x² + 4x = 0

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Add a constant
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x² + 4x + (4/2)² - (4/2)²  = 0   ← Add 2² to form perfect square

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Evaluate bracket
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x² + 4x + 2² - 2² = 0

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Form the perfect square
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(x + 2)² = 4 

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Square root both sides
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(x+2) =  √4

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Evaluate the square root
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(x+2) =  2

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Solve x 
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x = 2 - 2 or x = -2 - 2

x = 0 or -4

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The constant to add is 4 and the value of x = 0 or -4
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10,000 hope i ! : )