5x^2+6x+21=0

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Solution for 5x^2+6x+21=0 equation:


Simplifying
5x2 + 6x + 21 = 0

Reorder the terms:
21 + 6x + 5x2 = 0

Solving
21 + 6x + 5x2 = 0

Solving for variable 'x'.

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

Divide each side by '5'.
4.2 + 1.2x + x2 = 0

Move the constant term to the right:

Add '-4.2' to each side of the equation.
4.2 + 1.2x + -4.2 + x2 = 0 + -4.2

Reorder the terms:
4.2 + -4.2 + 1.2x + x2 = 0 + -4.2

Combine like terms: 4.2 + -4.2 = 0.0
0.0 + 1.2x + x2 = 0 + -4.2
1.2x + x2 = 0 + -4.2

Combine like terms: 0 + -4.2 = -4.2
1.2x + x2 = -4.2

The x term is 1.2x.  Take half its coefficient (0.6).
Square it (0.36) and add it to both sides.

Add '0.36' to each side of the equation.
1.2x + 0.36 + x2 = -4.2 + 0.36

Reorder the terms:
0.36 + 1.2x + x2 = -4.2 + 0.36

Combine like terms: -4.2 + 0.36 = -3.84
0.36 + 1.2x + x2 = -3.84

Factor a perfect square on the left side:
(x + 0.6)(x + 0.6) = -3.84

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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