-x^2+3x-21=0

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Solution for -x^2+3x-21=0 equation:


Simplifying
-1x2 + 3x + -21 = 0

Reorder the terms:
-21 + 3x + -1x2 = 0

Solving
-21 + 3x + -1x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
21 + -3x + x2 = 0

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -3x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + -3x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -3x + x2 = 0 + -21
-3x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
-3x + x2 = -21

The x term is -3x.  Take half its coefficient (-1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
-3x + 2.25 + x2 = -21 + 2.25

Reorder the terms:
2.25 + -3x + x2 = -21 + 2.25

Combine like terms: -21 + 2.25 = -18.75
2.25 + -3x + x2 = -18.75

Factor a perfect square on the left side:
(x + -1.5)(x + -1.5) = -18.75

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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