5x+x^2=81

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Solution for 5x+x^2=81 equation:


Simplifying
5x + x2 = 81

Solving
5x + x2 = 81

Solving for variable 'x'.

Reorder the terms:
-81 + 5x + x2 = 81 + -81

Combine like terms: 81 + -81 = 0
-81 + 5x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '81' to each side of the equation.
-81 + 5x + 81 + x2 = 0 + 81

Reorder the terms:
-81 + 81 + 5x + x2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + 5x + x2 = 0 + 81
5x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
5x + x2 = 81

The x term is 5x.  Take half its coefficient (2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
5x + 6.25 + x2 = 81 + 6.25

Reorder the terms:
6.25 + 5x + x2 = 81 + 6.25

Combine like terms: 81 + 6.25 = 87.25
6.25 + 5x + x2 = 87.25

Factor a perfect square on the left side:
(x + 2.5)(x + 2.5) = 87.25

Calculate the square root of the right side: 9.340770846

Break this problem into two subproblems by setting 
(x + 2.5) equal to 9.340770846 and -9.340770846.

Subproblem 1

x + 2.5 = 9.340770846 Simplifying x + 2.5 = 9.340770846 Reorder the terms: 2.5 + x = 9.340770846 Solving 2.5 + x = 9.340770846 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + x = 9.340770846 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + x = 9.340770846 + -2.5 x = 9.340770846 + -2.5 Combine like terms: 9.340770846 + -2.5 = 6.840770846 x = 6.840770846 Simplifying x = 6.840770846

Subproblem 2

x + 2.5 = -9.340770846 Simplifying x + 2.5 = -9.340770846 Reorder the terms: 2.5 + x = -9.340770846 Solving 2.5 + x = -9.340770846 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + x = -9.340770846 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + x = -9.340770846 + -2.5 x = -9.340770846 + -2.5 Combine like terms: -9.340770846 + -2.5 = -11.840770846 x = -11.840770846 Simplifying x = -11.840770846

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.840770846, -11.840770846}

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