x^2+3x^2-9x-18=0

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Solution for x^2+3x^2-9x-18=0 equation:


Simplifying
x2 + 3x2 + -9x + -18 = 0

Reorder the terms:
-18 + -9x + x2 + 3x2 = 0

Combine like terms: x2 + 3x2 = 4x2
-18 + -9x + 4x2 = 0

Solving
-18 + -9x + 4x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
4 the coefficient of the squared term: 

Divide each side by '4'.
-4.5 + -2.25x + x2 = 0

Move the constant term to the right:

Add '4.5' to each side of the equation.
-4.5 + -2.25x + 4.5 + x2 = 0 + 4.5

Reorder the terms:
-4.5 + 4.5 + -2.25x + x2 = 0 + 4.5

Combine like terms: -4.5 + 4.5 = 0.0
0.0 + -2.25x + x2 = 0 + 4.5
-2.25x + x2 = 0 + 4.5

Combine like terms: 0 + 4.5 = 4.5
-2.25x + x2 = 4.5

The x term is -2.25x.  Take half its coefficient (-1.125).
Square it (1.265625) and add it to both sides.

Add '1.265625' to each side of the equation.
-2.25x + 1.265625 + x2 = 4.5 + 1.265625

Reorder the terms:
1.265625 + -2.25x + x2 = 4.5 + 1.265625

Combine like terms: 4.5 + 1.265625 = 5.765625
1.265625 + -2.25x + x2 = 5.765625

Factor a perfect square on the left side:
(x + -1.125)(x + -1.125) = 5.765625

Calculate the square root of the right side: 2.401171589

Break this problem into two subproblems by setting 
(x + -1.125) equal to 2.401171589 and -2.401171589.

Subproblem 1

x + -1.125 = 2.401171589 Simplifying x + -1.125 = 2.401171589 Reorder the terms: -1.125 + x = 2.401171589 Solving -1.125 + x = 2.401171589 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.125' to each side of the equation. -1.125 + 1.125 + x = 2.401171589 + 1.125 Combine like terms: -1.125 + 1.125 = 0.000 0.000 + x = 2.401171589 + 1.125 x = 2.401171589 + 1.125 Combine like terms: 2.401171589 + 1.125 = 3.526171589 x = 3.526171589 Simplifying x = 3.526171589

Subproblem 2

x + -1.125 = -2.401171589 Simplifying x + -1.125 = -2.401171589 Reorder the terms: -1.125 + x = -2.401171589 Solving -1.125 + x = -2.401171589 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.125' to each side of the equation. -1.125 + 1.125 + x = -2.401171589 + 1.125 Combine like terms: -1.125 + 1.125 = 0.000 0.000 + x = -2.401171589 + 1.125 x = -2.401171589 + 1.125 Combine like terms: -2.401171589 + 1.125 = -1.276171589 x = -1.276171589 Simplifying x = -1.276171589

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.526171589, -1.276171589}

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