-x^2+x+81=0

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


Simplifying
-1x2 + x + 81 = 0

Reorder the terms:
81 + x + -1x2 = 0

Solving
81 + x + -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'.
-81 + -1x + x2 = 0

Move the constant term to the right:

Add '81' to each side of the equation.
-81 + -1x + 81 + x2 = 0 + 81

Reorder the terms:
-81 + 81 + -1x + x2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + -1x + x2 = 0 + 81
-1x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
-1x + x2 = 81

The x term is x.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1x + 0.25 + x2 = 81 + 0.25

Reorder the terms:
0.25 + -1x + x2 = 81 + 0.25

Combine like terms: 81 + 0.25 = 81.25
0.25 + -1x + x2 = 81.25

Factor a perfect square on the left side:
(x + 0.5)(x + 0.5) = 81.25

Calculate the square root of the right side: 9.013878189

Break this problem into two subproblems by setting 
(x + 0.5) equal to 9.013878189 and -9.013878189.

Subproblem 1

x + 0.5 = 9.013878189 Simplifying x + 0.5 = 9.013878189 Reorder the terms: 0.5 + x = 9.013878189 Solving 0.5 + x = 9.013878189 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + x = 9.013878189 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + x = 9.013878189 + -0.5 x = 9.013878189 + -0.5 Combine like terms: 9.013878189 + -0.5 = 8.513878189 x = 8.513878189 Simplifying x = 8.513878189

Subproblem 2

x + 0.5 = -9.013878189 Simplifying x + 0.5 = -9.013878189 Reorder the terms: 0.5 + x = -9.013878189 Solving 0.5 + x = -9.013878189 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + x = -9.013878189 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + x = -9.013878189 + -0.5 x = -9.013878189 + -0.5 Combine like terms: -9.013878189 + -0.5 = -9.513878189 x = -9.513878189 Simplifying x = -9.513878189

Solution

The solution to the problem is based on the solutions from the subproblems. x = {8.513878189, -9.513878189}

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