x^2+20x-81=0

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Solution for x^2+20x-81=0 equation:


Simplifying
x2 + 20x + -81 = 0

Reorder the terms:
-81 + 20x + x2 = 0

Solving
-81 + 20x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '81' to each side of the equation.
-81 + 20x + 81 + x2 = 0 + 81

Reorder the terms:
-81 + 81 + 20x + x2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + 20x + x2 = 0 + 81
20x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
20x + x2 = 81

The x term is 20x.  Take half its coefficient (10).
Square it (100) and add it to both sides.

Add '100' to each side of the equation.
20x + 100 + x2 = 81 + 100

Reorder the terms:
100 + 20x + x2 = 81 + 100

Combine like terms: 81 + 100 = 181
100 + 20x + x2 = 181

Factor a perfect square on the left side:
(x + 10)(x + 10) = 181

Calculate the square root of the right side: 13.453624047

Break this problem into two subproblems by setting 
(x + 10) equal to 13.453624047 and -13.453624047.

Subproblem 1

x + 10 = 13.453624047 Simplifying x + 10 = 13.453624047 Reorder the terms: 10 + x = 13.453624047 Solving 10 + x = 13.453624047 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10' to each side of the equation. 10 + -10 + x = 13.453624047 + -10 Combine like terms: 10 + -10 = 0 0 + x = 13.453624047 + -10 x = 13.453624047 + -10 Combine like terms: 13.453624047 + -10 = 3.453624047 x = 3.453624047 Simplifying x = 3.453624047

Subproblem 2

x + 10 = -13.453624047 Simplifying x + 10 = -13.453624047 Reorder the terms: 10 + x = -13.453624047 Solving 10 + x = -13.453624047 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10' to each side of the equation. 10 + -10 + x = -13.453624047 + -10 Combine like terms: 10 + -10 = 0 0 + x = -13.453624047 + -10 x = -13.453624047 + -10 Combine like terms: -13.453624047 + -10 = -23.453624047 x = -23.453624047 Simplifying x = -23.453624047

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.453624047, -23.453624047}

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