x^2+7x=81

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Solution for x^2+7x=81 equation:


Simplifying
x2 + 7x = 81

Reorder the terms:
7x + x2 = 81

Solving
7x + x2 = 81

Solving for variable 'x'.

Reorder the terms:
-81 + 7x + x2 = 81 + -81

Combine like terms: 81 + -81 = 0
-81 + 7x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '81' to each side of the equation.
-81 + 7x + 81 + x2 = 0 + 81

Reorder the terms:
-81 + 81 + 7x + x2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + 7x + x2 = 0 + 81
7x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
7x + x2 = 81

The x term is 7x.  Take half its coefficient (3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
7x + 12.25 + x2 = 81 + 12.25

Reorder the terms:
12.25 + 7x + x2 = 81 + 12.25

Combine like terms: 81 + 12.25 = 93.25
12.25 + 7x + x2 = 93.25

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 93.25

Calculate the square root of the right side: 9.656603958

Break this problem into two subproblems by setting 
(x + 3.5) equal to 9.656603958 and -9.656603958.

Subproblem 1

x + 3.5 = 9.656603958 Simplifying x + 3.5 = 9.656603958 Reorder the terms: 3.5 + x = 9.656603958 Solving 3.5 + x = 9.656603958 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.5' to each side of the equation. 3.5 + -3.5 + x = 9.656603958 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = 9.656603958 + -3.5 x = 9.656603958 + -3.5 Combine like terms: 9.656603958 + -3.5 = 6.156603958 x = 6.156603958 Simplifying x = 6.156603958

Subproblem 2

x + 3.5 = -9.656603958 Simplifying x + 3.5 = -9.656603958 Reorder the terms: 3.5 + x = -9.656603958 Solving 3.5 + x = -9.656603958 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.5' to each side of the equation. 3.5 + -3.5 + x = -9.656603958 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = -9.656603958 + -3.5 x = -9.656603958 + -3.5 Combine like terms: -9.656603958 + -3.5 = -13.156603958 x = -13.156603958 Simplifying x = -13.156603958

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.156603958, -13.156603958}

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