21+3x-x^2=12

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Solution for 21+3x-x^2=12 equation:


Simplifying
21 + 3x + -1x2 = 12

Solving
21 + 3x + -1x2 = 12

Solving for variable 'x'.

Reorder the terms:
21 + -12 + 3x + -1x2 = 12 + -12

Combine like terms: 21 + -12 = 9
9 + 3x + -1x2 = 12 + -12

Combine like terms: 12 + -12 = 0
9 + 3x + -1x2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
-9 + -3x + x2 = 0

Move the constant term to the right:

Add '9' to each side of the equation.
-9 + -3x + 9 + x2 = 0 + 9

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

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

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

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 = 9 + 2.25

Reorder the terms:
2.25 + -3x + x2 = 9 + 2.25

Combine like terms: 9 + 2.25 = 11.25
2.25 + -3x + x2 = 11.25

Factor a perfect square on the left side:
(x + -1.5)(x + -1.5) = 11.25

Calculate the square root of the right side: 3.354101966

Break this problem into two subproblems by setting 
(x + -1.5) equal to 3.354101966 and -3.354101966.

Subproblem 1

x + -1.5 = 3.354101966 Simplifying x + -1.5 = 3.354101966 Reorder the terms: -1.5 + x = 3.354101966 Solving -1.5 + x = 3.354101966 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 = 3.354101966 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = 3.354101966 + 1.5 x = 3.354101966 + 1.5 Combine like terms: 3.354101966 + 1.5 = 4.854101966 x = 4.854101966 Simplifying x = 4.854101966

Subproblem 2

x + -1.5 = -3.354101966 Simplifying x + -1.5 = -3.354101966 Reorder the terms: -1.5 + x = -3.354101966 Solving -1.5 + x = -3.354101966 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 = -3.354101966 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = -3.354101966 + 1.5 x = -3.354101966 + 1.5 Combine like terms: -3.354101966 + 1.5 = -1.854101966 x = -1.854101966 Simplifying x = -1.854101966

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.854101966, -1.854101966}

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