2x^2+3x=81

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Solution for 2x^2+3x=81 equation:


Simplifying
2x2 + 3x = 81

Reorder the terms:
3x + 2x2 = 81

Solving
3x + 2x2 = 81

Solving for variable 'x'.

Reorder the terms:
-81 + 3x + 2x2 = 81 + -81

Combine like terms: 81 + -81 = 0
-81 + 3x + 2x2 = 0

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

Divide each side by '2'.
-40.5 + 1.5x + x2 = 0

Move the constant term to the right:

Add '40.5' to each side of the equation.
-40.5 + 1.5x + 40.5 + x2 = 0 + 40.5

Reorder the terms:
-40.5 + 40.5 + 1.5x + x2 = 0 + 40.5

Combine like terms: -40.5 + 40.5 = 0.0
0.0 + 1.5x + x2 = 0 + 40.5
1.5x + x2 = 0 + 40.5

Combine like terms: 0 + 40.5 = 40.5
1.5x + x2 = 40.5

The x term is 1.5x.  Take half its coefficient (0.75).
Square it (0.5625) and add it to both sides.

Add '0.5625' to each side of the equation.
1.5x + 0.5625 + x2 = 40.5 + 0.5625

Reorder the terms:
0.5625 + 1.5x + x2 = 40.5 + 0.5625

Combine like terms: 40.5 + 0.5625 = 41.0625
0.5625 + 1.5x + x2 = 41.0625

Factor a perfect square on the left side:
(x + 0.75)(x + 0.75) = 41.0625

Calculate the square root of the right side: 6.408002809

Break this problem into two subproblems by setting 
(x + 0.75) equal to 6.408002809 and -6.408002809.

Subproblem 1

x + 0.75 = 6.408002809 Simplifying x + 0.75 = 6.408002809 Reorder the terms: 0.75 + x = 6.408002809 Solving 0.75 + x = 6.408002809 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.75' to each side of the equation. 0.75 + -0.75 + x = 6.408002809 + -0.75 Combine like terms: 0.75 + -0.75 = 0.00 0.00 + x = 6.408002809 + -0.75 x = 6.408002809 + -0.75 Combine like terms: 6.408002809 + -0.75 = 5.658002809 x = 5.658002809 Simplifying x = 5.658002809

Subproblem 2

x + 0.75 = -6.408002809 Simplifying x + 0.75 = -6.408002809 Reorder the terms: 0.75 + x = -6.408002809 Solving 0.75 + x = -6.408002809 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.75' to each side of the equation. 0.75 + -0.75 + x = -6.408002809 + -0.75 Combine like terms: 0.75 + -0.75 = 0.00 0.00 + x = -6.408002809 + -0.75 x = -6.408002809 + -0.75 Combine like terms: -6.408002809 + -0.75 = -7.158002809 x = -7.158002809 Simplifying x = -7.158002809

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.658002809, -7.158002809}

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