.4x^2+.6x-7=0

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Solution for .4x^2+.6x-7=0 equation:


Simplifying
0.4x2 + 0.6x + -7 = 0

Reorder the terms:
-7 + 0.6x + 0.4x2 = 0

Solving
-7 + 0.6x + 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'.
-17.5 + 1.5x + x2 = 0

Move the constant term to the right:

Add '17.5' to each side of the equation.
-17.5 + 1.5x + 17.5 + x2 = 0 + 17.5

Reorder the terms:
-17.5 + 17.5 + 1.5x + x2 = 0 + 17.5

Combine like terms: -17.5 + 17.5 = 0.0
0.0 + 1.5x + x2 = 0 + 17.5
1.5x + x2 = 0 + 17.5

Combine like terms: 0 + 17.5 = 17.5
1.5x + x2 = 17.5

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 = 17.5 + 0.5625

Reorder the terms:
0.5625 + 1.5x + x2 = 17.5 + 0.5625

Combine like terms: 17.5 + 0.5625 = 18.0625
0.5625 + 1.5x + x2 = 18.0625

Factor a perfect square on the left side:
(x + 0.75)(x + 0.75) = 18.0625

Calculate the square root of the right side: 4.25

Break this problem into two subproblems by setting 
(x + 0.75) equal to 4.25 and -4.25.

Subproblem 1

x + 0.75 = 4.25 Simplifying x + 0.75 = 4.25 Reorder the terms: 0.75 + x = 4.25 Solving 0.75 + x = 4.25 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 = 4.25 + -0.75 Combine like terms: 0.75 + -0.75 = 0.00 0.00 + x = 4.25 + -0.75 x = 4.25 + -0.75 Combine like terms: 4.25 + -0.75 = 3.5 x = 3.5 Simplifying x = 3.5

Subproblem 2

x + 0.75 = -4.25 Simplifying x + 0.75 = -4.25 Reorder the terms: 0.75 + x = -4.25 Solving 0.75 + x = -4.25 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 = -4.25 + -0.75 Combine like terms: 0.75 + -0.75 = 0.00 0.00 + x = -4.25 + -0.75 x = -4.25 + -0.75 Combine like terms: -4.25 + -0.75 = -5 x = -5 Simplifying x = -5

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.5, -5}

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