0.4*x^2+3*x-135=0

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Solution for 0.4*x^2+3*x-135=0 equation:


Simplifying
0.4x2 + 3x + -135 = 0

Reorder the terms:
-135 + 3x + 0.4x2 = 0

Solving
-135 + 3x + 0.4x2 = 0

Solving for variable 'x'.

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

Divide each side by '0.4'.
-337.5 + 7.5x + x2 = 0

Move the constant term to the right:

Add '337.5' to each side of the equation.
-337.5 + 7.5x + 337.5 + x2 = 0 + 337.5

Reorder the terms:
-337.5 + 337.5 + 7.5x + x2 = 0 + 337.5

Combine like terms: -337.5 + 337.5 = 0.0
0.0 + 7.5x + x2 = 0 + 337.5
7.5x + x2 = 0 + 337.5

Combine like terms: 0 + 337.5 = 337.5
7.5x + x2 = 337.5

The x term is 7.5x.  Take half its coefficient (3.75).
Square it (14.0625) and add it to both sides.

Add '14.0625' to each side of the equation.
7.5x + 14.0625 + x2 = 337.5 + 14.0625

Reorder the terms:
14.0625 + 7.5x + x2 = 337.5 + 14.0625

Combine like terms: 337.5 + 14.0625 = 351.5625
14.0625 + 7.5x + x2 = 351.5625

Factor a perfect square on the left side:
(x + 3.75)(x + 3.75) = 351.5625

Calculate the square root of the right side: 18.75

Break this problem into two subproblems by setting 
(x + 3.75) equal to 18.75 and -18.75.

Subproblem 1

x + 3.75 = 18.75 Simplifying x + 3.75 = 18.75 Reorder the terms: 3.75 + x = 18.75 Solving 3.75 + x = 18.75 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.75' to each side of the equation. 3.75 + -3.75 + x = 18.75 + -3.75 Combine like terms: 3.75 + -3.75 = 0.00 0.00 + x = 18.75 + -3.75 x = 18.75 + -3.75 Combine like terms: 18.75 + -3.75 = 15 x = 15 Simplifying x = 15

Subproblem 2

x + 3.75 = -18.75 Simplifying x + 3.75 = -18.75 Reorder the terms: 3.75 + x = -18.75 Solving 3.75 + x = -18.75 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.75' to each side of the equation. 3.75 + -3.75 + x = -18.75 + -3.75 Combine like terms: 3.75 + -3.75 = 0.00 0.00 + x = -18.75 + -3.75 x = -18.75 + -3.75 Combine like terms: -18.75 + -3.75 = -22.5 x = -22.5 Simplifying x = -22.5

Solution

The solution to the problem is based on the solutions from the subproblems. x = {15, -22.5}

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