4x^2+8x+21=0

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Solution for 4x^2+8x+21=0 equation:


Simplifying
4x2 + 8x + 21 = 0

Reorder the terms:
21 + 8x + 4x2 = 0

Solving
21 + 8x + 4x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
4 the coefficient of the squared term: 

Divide each side by '4'.
5.25 + 2x + x2 = 0

Move the constant term to the right:

Add '-5.25' to each side of the equation.
5.25 + 2x + -5.25 + x2 = 0 + -5.25

Reorder the terms:
5.25 + -5.25 + 2x + x2 = 0 + -5.25

Combine like terms: 5.25 + -5.25 = 0.00
0.00 + 2x + x2 = 0 + -5.25
2x + x2 = 0 + -5.25

Combine like terms: 0 + -5.25 = -5.25
2x + x2 = -5.25

The x term is 2x.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2x + 1 + x2 = -5.25 + 1

Reorder the terms:
1 + 2x + x2 = -5.25 + 1

Combine like terms: -5.25 + 1 = -4.25
1 + 2x + x2 = -4.25

Factor a perfect square on the left side:
(x + 1)(x + 1) = -4.25

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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