5x^2-8x+21=0

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Solution for 5x^2-8x+21=0 equation:


Simplifying
5x2 + -8x + 21 = 0

Reorder the terms:
21 + -8x + 5x2 = 0

Solving
21 + -8x + 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 + -1.6x + x2 = 0

Move the constant term to the right:

Add '-4.2' to each side of the equation.
4.2 + -1.6x + -4.2 + x2 = 0 + -4.2

Reorder the terms:
4.2 + -4.2 + -1.6x + x2 = 0 + -4.2

Combine like terms: 4.2 + -4.2 = 0.0
0.0 + -1.6x + x2 = 0 + -4.2
-1.6x + x2 = 0 + -4.2

Combine like terms: 0 + -4.2 = -4.2
-1.6x + x2 = -4.2

The x term is -1.6x.  Take half its coefficient (-0.8).
Square it (0.64) and add it to both sides.

Add '0.64' to each side of the equation.
-1.6x + 0.64 + x2 = -4.2 + 0.64

Reorder the terms:
0.64 + -1.6x + x2 = -4.2 + 0.64

Combine like terms: -4.2 + 0.64 = -3.56
0.64 + -1.6x + x2 = -3.56

Factor a perfect square on the left side:
(x + -0.8)(x + -0.8) = -3.56

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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