-x(x+4)=21

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Solution for -x(x+4)=21 equation: 


Simplifying
-1x(x + 4) = 21

Reorder the terms:
-1x(4 + x) = 21
(4 * -1x + x * -1x) = 21
(-4x + -1x2) = 21

Solving
-4x + -1x2 = 21

Solving for variable 'x'.

Reorder the terms:
-21 + -4x + -1x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + -4x + -1x2 = 0

Factor out the Greatest Common Factor (GCF), '-1'.
-1(21 + 4x + x2) = 0

Ignore the factor -1.

Subproblem 1
Set the factor '(21 + 4x + x2)' equal to zero and attempt to solve:

Simplifying
21 + 4x + x2 = 0

Solving
21 + 4x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + 4x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + 4x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + 4x + x2 = 0 + -21
4x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
4x + x2 = -21

The x term is 4x.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4x + 4 + x2 = -21 + 4

Reorder the terms:
4 + 4x + x2 = -21 + 4

Combine like terms: -21 + 4 = -17
4 + 4x + x2 = -17

Factor a perfect square on the left side:
(x + 2)(x + 2) = -17

Can't calculate square root of the right side.

The solution to this equation could not be determined.

This subproblem is being ignored because a solution could not be determined.

The solution to this equation could not be determined.

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