x^2+3x=128

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Solution for x^2+3x=128 equation:


Simplifying
x2 + 3x = 128

Reorder the terms:
3x + x2 = 128

Solving
3x + x2 = 128

Solving for variable 'x'.

Reorder the terms:
-128 + 3x + x2 = 128 + -128

Combine like terms: 128 + -128 = 0
-128 + 3x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '128' to each side of the equation.
-128 + 3x + 128 + x2 = 0 + 128

Reorder the terms:
-128 + 128 + 3x + x2 = 0 + 128

Combine like terms: -128 + 128 = 0
0 + 3x + x2 = 0 + 128
3x + x2 = 0 + 128

Combine like terms: 0 + 128 = 128
3x + x2 = 128

The x term is 3x.  Take half its coefficient (1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
3x + 2.25 + x2 = 128 + 2.25

Reorder the terms:
2.25 + 3x + x2 = 128 + 2.25

Combine like terms: 128 + 2.25 = 130.25
2.25 + 3x + x2 = 130.25

Factor a perfect square on the left side:
(x + 1.5)(x + 1.5) = 130.25

Calculate the square root of the right side: 11.412712211

Break this problem into two subproblems by setting 
(x + 1.5) equal to 11.412712211 and -11.412712211.

Subproblem 1

x + 1.5 = 11.412712211 Simplifying x + 1.5 = 11.412712211 Reorder the terms: 1.5 + x = 11.412712211 Solving 1.5 + x = 11.412712211 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.5' to each side of the equation. 1.5 + -1.5 + x = 11.412712211 + -1.5 Combine like terms: 1.5 + -1.5 = 0.0 0.0 + x = 11.412712211 + -1.5 x = 11.412712211 + -1.5 Combine like terms: 11.412712211 + -1.5 = 9.912712211 x = 9.912712211 Simplifying x = 9.912712211

Subproblem 2

x + 1.5 = -11.412712211 Simplifying x + 1.5 = -11.412712211 Reorder the terms: 1.5 + x = -11.412712211 Solving 1.5 + x = -11.412712211 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.5' to each side of the equation. 1.5 + -1.5 + x = -11.412712211 + -1.5 Combine like terms: 1.5 + -1.5 = 0.0 0.0 + x = -11.412712211 + -1.5 x = -11.412712211 + -1.5 Combine like terms: -11.412712211 + -1.5 = -12.912712211 x = -12.912712211 Simplifying x = -12.912712211

Solution

The solution to the problem is based on the solutions from the subproblems. x = {9.912712211, -12.912712211}

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