2x^2+8x+21=0

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


Simplifying
2x2 + 8x + 21 = 0

Reorder the terms:
21 + 8x + 2x2 = 0

Solving
21 + 8x + 2x2 = 0

Solving for variable 'x'.

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

Divide each side by '2'.
10.5 + 4x + x2 = 0

Move the constant term to the right:

Add '-10.5' to each side of the equation.
10.5 + 4x + -10.5 + x2 = 0 + -10.5

Reorder the terms:
10.5 + -10.5 + 4x + x2 = 0 + -10.5

Combine like terms: 10.5 + -10.5 = 0.0
0.0 + 4x + x2 = 0 + -10.5
4x + x2 = 0 + -10.5

Combine like terms: 0 + -10.5 = -10.5
4x + x2 = -10.5

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 = -10.5 + 4

Reorder the terms:
4 + 4x + x2 = -10.5 + 4

Combine like terms: -10.5 + 4 = -6.5
4 + 4x + x2 = -6.5

Factor a perfect square on the left side:
(x + 2)(x + 2) = -6.5

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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