-x^2-21x+20=0

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Solution for -x^2-21x+20=0 equation:


Simplifying
-1x2 + -21x + 20 = 0

Reorder the terms:
20 + -21x + -1x2 = 0

Solving
20 + -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'.
-20 + 21x + x2 = 0

Move the constant term to the right:

Add '20' to each side of the equation.
-20 + 21x + 20 + x2 = 0 + 20

Reorder the terms:
-20 + 20 + 21x + x2 = 0 + 20

Combine like terms: -20 + 20 = 0
0 + 21x + x2 = 0 + 20
21x + x2 = 0 + 20

Combine like terms: 0 + 20 = 20
21x + x2 = 20

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 = 20 + 110.25

Reorder the terms:
110.25 + 21x + x2 = 20 + 110.25

Combine like terms: 20 + 110.25 = 130.25
110.25 + 21x + x2 = 130.25

Factor a perfect square on the left side:
(x + 10.5)(x + 10.5) = 130.25

Calculate the square root of the right side: 11.412712211

Break this problem into two subproblems by setting 
(x + 10.5) equal to 11.412712211 and -11.412712211.

Subproblem 1

x + 10.5 = 11.412712211 Simplifying x + 10.5 = 11.412712211 Reorder the terms: 10.5 + x = 11.412712211 Solving 10.5 + x = 11.412712211 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 = 11.412712211 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = 11.412712211 + -10.5 x = 11.412712211 + -10.5 Combine like terms: 11.412712211 + -10.5 = 0.912712211 x = 0.912712211 Simplifying x = 0.912712211

Subproblem 2

x + 10.5 = -11.412712211 Simplifying x + 10.5 = -11.412712211 Reorder the terms: 10.5 + x = -11.412712211 Solving 10.5 + x = -11.412712211 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 = -11.412712211 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = -11.412712211 + -10.5 x = -11.412712211 + -10.5 Combine like terms: -11.412712211 + -10.5 = -21.912712211 x = -21.912712211 Simplifying x = -21.912712211

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.912712211, -21.912712211}

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