0.4x^2-5x+15=0

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Solution for 0.4x^2-5x+15=0 equation:


Simplifying
0.4x2 + -5x + 15 = 0

Reorder the terms:
15 + -5x + 0.4x2 = 0

Solving
15 + -5x + 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'.
37.5 + -12.5x + x2 = 0

Move the constant term to the right:

Add '-37.5' to each side of the equation.
37.5 + -12.5x + -37.5 + x2 = 0 + -37.5

Reorder the terms:
37.5 + -37.5 + -12.5x + x2 = 0 + -37.5

Combine like terms: 37.5 + -37.5 = 0.0
0.0 + -12.5x + x2 = 0 + -37.5
-12.5x + x2 = 0 + -37.5

Combine like terms: 0 + -37.5 = -37.5
-12.5x + x2 = -37.5

The x term is -12.5x.  Take half its coefficient (-6.25).
Square it (39.0625) and add it to both sides.

Add '39.0625' to each side of the equation.
-12.5x + 39.0625 + x2 = -37.5 + 39.0625

Reorder the terms:
39.0625 + -12.5x + x2 = -37.5 + 39.0625

Combine like terms: -37.5 + 39.0625 = 1.5625
39.0625 + -12.5x + x2 = 1.5625

Factor a perfect square on the left side:
(x + -6.25)(x + -6.25) = 1.5625

Calculate the square root of the right side: 1.25

Break this problem into two subproblems by setting 
(x + -6.25) equal to 1.25 and -1.25.

Subproblem 1

x + -6.25 = 1.25 Simplifying x + -6.25 = 1.25 Reorder the terms: -6.25 + x = 1.25 Solving -6.25 + x = 1.25 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '6.25' to each side of the equation. -6.25 + 6.25 + x = 1.25 + 6.25 Combine like terms: -6.25 + 6.25 = 0.00 0.00 + x = 1.25 + 6.25 x = 1.25 + 6.25 Combine like terms: 1.25 + 6.25 = 7.5 x = 7.5 Simplifying x = 7.5

Subproblem 2

x + -6.25 = -1.25 Simplifying x + -6.25 = -1.25 Reorder the terms: -6.25 + x = -1.25 Solving -6.25 + x = -1.25 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '6.25' to each side of the equation. -6.25 + 6.25 + x = -1.25 + 6.25 Combine like terms: -6.25 + 6.25 = 0.00 0.00 + x = -1.25 + 6.25 x = -1.25 + 6.25 Combine like terms: -1.25 + 6.25 = 5 x = 5 Simplifying x = 5

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7.5, 5}

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