x^2+3x+12=90

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Solution for x^2+3x+12=90 equation:


Simplifying
x2 + 3x + 12 = 90

Reorder the terms:
12 + 3x + x2 = 90

Solving
12 + 3x + x2 = 90

Solving for variable 'x'.

Reorder the terms:
12 + -90 + 3x + x2 = 90 + -90

Combine like terms: 12 + -90 = -78
-78 + 3x + x2 = 90 + -90

Combine like terms: 90 + -90 = 0
-78 + 3x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '78' to each side of the equation.
-78 + 3x + 78 + x2 = 0 + 78

Reorder the terms:
-78 + 78 + 3x + x2 = 0 + 78

Combine like terms: -78 + 78 = 0
0 + 3x + x2 = 0 + 78
3x + x2 = 0 + 78

Combine like terms: 0 + 78 = 78
3x + x2 = 78

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 = 78 + 2.25

Reorder the terms:
2.25 + 3x + x2 = 78 + 2.25

Combine like terms: 78 + 2.25 = 80.25
2.25 + 3x + x2 = 80.25

Factor a perfect square on the left side:
(x + 1.5)(x + 1.5) = 80.25

Calculate the square root of the right side: 8.958236434

Break this problem into two subproblems by setting 
(x + 1.5) equal to 8.958236434 and -8.958236434.

Subproblem 1

x + 1.5 = 8.958236434 Simplifying x + 1.5 = 8.958236434 Reorder the terms: 1.5 + x = 8.958236434 Solving 1.5 + x = 8.958236434 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 = 8.958236434 + -1.5 Combine like terms: 1.5 + -1.5 = 0.0 0.0 + x = 8.958236434 + -1.5 x = 8.958236434 + -1.5 Combine like terms: 8.958236434 + -1.5 = 7.458236434 x = 7.458236434 Simplifying x = 7.458236434

Subproblem 2

x + 1.5 = -8.958236434 Simplifying x + 1.5 = -8.958236434 Reorder the terms: 1.5 + x = -8.958236434 Solving 1.5 + x = -8.958236434 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 = -8.958236434 + -1.5 Combine like terms: 1.5 + -1.5 = 0.0 0.0 + x = -8.958236434 + -1.5 x = -8.958236434 + -1.5 Combine like terms: -8.958236434 + -1.5 = -10.458236434 x = -10.458236434 Simplifying x = -10.458236434

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.458236434, -10.458236434}

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