4x^2-36x=81

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Solution for 4x^2-36x=81 equation:


Simplifying
4x2 + -36x = 81

Reorder the terms:
-36x + 4x2 = 81

Solving
-36x + 4x2 = 81

Solving for variable 'x'.

Reorder the terms:
-81 + -36x + 4x2 = 81 + -81

Combine like terms: 81 + -81 = 0
-81 + -36x + 4x2 = 0

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

Divide each side by '4'.
-20.25 + -9x + x2 = 0

Move the constant term to the right:

Add '20.25' to each side of the equation.
-20.25 + -9x + 20.25 + x2 = 0 + 20.25

Reorder the terms:
-20.25 + 20.25 + -9x + x2 = 0 + 20.25

Combine like terms: -20.25 + 20.25 = 0.00
0.00 + -9x + x2 = 0 + 20.25
-9x + x2 = 0 + 20.25

Combine like terms: 0 + 20.25 = 20.25
-9x + x2 = 20.25

The x term is -9x.  Take half its coefficient (-4.5).
Square it (20.25) and add it to both sides.

Add '20.25' to each side of the equation.
-9x + 20.25 + x2 = 20.25 + 20.25

Reorder the terms:
20.25 + -9x + x2 = 20.25 + 20.25

Combine like terms: 20.25 + 20.25 = 40.5
20.25 + -9x + x2 = 40.5

Factor a perfect square on the left side:
(x + -4.5)(x + -4.5) = 40.5

Calculate the square root of the right side: 6.363961031

Break this problem into two subproblems by setting 
(x + -4.5) equal to 6.363961031 and -6.363961031.

Subproblem 1

x + -4.5 = 6.363961031 Simplifying x + -4.5 = 6.363961031 Reorder the terms: -4.5 + x = 6.363961031 Solving -4.5 + x = 6.363961031 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4.5' to each side of the equation. -4.5 + 4.5 + x = 6.363961031 + 4.5 Combine like terms: -4.5 + 4.5 = 0.0 0.0 + x = 6.363961031 + 4.5 x = 6.363961031 + 4.5 Combine like terms: 6.363961031 + 4.5 = 10.863961031 x = 10.863961031 Simplifying x = 10.863961031

Subproblem 2

x + -4.5 = -6.363961031 Simplifying x + -4.5 = -6.363961031 Reorder the terms: -4.5 + x = -6.363961031 Solving -4.5 + x = -6.363961031 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4.5' to each side of the equation. -4.5 + 4.5 + x = -6.363961031 + 4.5 Combine like terms: -4.5 + 4.5 = 0.0 0.0 + x = -6.363961031 + 4.5 x = -6.363961031 + 4.5 Combine like terms: -6.363961031 + 4.5 = -1.863961031 x = -1.863961031 Simplifying x = -1.863961031

Solution

The solution to the problem is based on the solutions from the subproblems. x = {10.863961031, -1.863961031}

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