-x^2-21x+80=0

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Solution for -x^2-21x+80=0 equation:


Simplifying
-1x2 + -21x + 80 = 0

Reorder the terms:
80 + -21x + -1x2 = 0

Solving
80 + -21x + -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'.
-80 + 21x + x2 = 0

Move the constant term to the right:

Add '80' to each side of the equation.
-80 + 21x + 80 + x2 = 0 + 80

Reorder the terms:
-80 + 80 + 21x + x2 = 0 + 80

Combine like terms: -80 + 80 = 0
0 + 21x + x2 = 0 + 80
21x + x2 = 0 + 80

Combine like terms: 0 + 80 = 80
21x + x2 = 80

The x term is 21x.  Take half its coefficient (10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
21x + 110.25 + x2 = 80 + 110.25

Reorder the terms:
110.25 + 21x + x2 = 80 + 110.25

Combine like terms: 80 + 110.25 = 190.25
110.25 + 21x + x2 = 190.25

Factor a perfect square on the left side:
(x + 10.5)(x + 10.5) = 190.25

Calculate the square root of the right side: 13.793114224

Break this problem into two subproblems by setting 
(x + 10.5) equal to 13.793114224 and -13.793114224.

Subproblem 1

x + 10.5 = 13.793114224 Simplifying x + 10.5 = 13.793114224 Reorder the terms: 10.5 + x = 13.793114224 Solving 10.5 + x = 13.793114224 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = 13.793114224 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = 13.793114224 + -10.5 x = 13.793114224 + -10.5 Combine like terms: 13.793114224 + -10.5 = 3.293114224 x = 3.293114224 Simplifying x = 3.293114224

Subproblem 2

x + 10.5 = -13.793114224 Simplifying x + 10.5 = -13.793114224 Reorder the terms: 10.5 + x = -13.793114224 Solving 10.5 + x = -13.793114224 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = -13.793114224 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = -13.793114224 + -10.5 x = -13.793114224 + -10.5 Combine like terms: -13.793114224 + -10.5 = -24.293114224 x = -24.293114224 Simplifying x = -24.293114224

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.293114224, -24.293114224}

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