.4x^2-1.6x-8.4=0

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Solution for .4x^2-1.6x-8.4=0 equation:


Simplifying
0.4x2 + -1.6x + -8.4 = 0

Reorder the terms:
-8.4 + -1.6x + 0.4x2 = 0

Solving
-8.4 + -1.6x + 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'.
-21 + -4x + x2 = 0

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + -4x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + -4x + x2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -4x + x2 = 0 + 21
-4x + x2 = 0 + 21

Combine like terms: 0 + 21 = 21
-4x + x2 = 21

The x term is -4x.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4x + 4 + x2 = 21 + 4

Reorder the terms:
4 + -4x + x2 = 21 + 4

Combine like terms: 21 + 4 = 25
4 + -4x + x2 = 25

Factor a perfect square on the left side:
(x + -2)(x + -2) = 25

Calculate the square root of the right side: 5

Break this problem into two subproblems by setting 
(x + -2) equal to 5 and -5.

Subproblem 1

x + -2 = 5 Simplifying x + -2 = 5 Reorder the terms: -2 + x = 5 Solving -2 + x = 5 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + x = 5 + 2 Combine like terms: -2 + 2 = 0 0 + x = 5 + 2 x = 5 + 2 Combine like terms: 5 + 2 = 7 x = 7 Simplifying x = 7

Subproblem 2

x + -2 = -5 Simplifying x + -2 = -5 Reorder the terms: -2 + x = -5 Solving -2 + x = -5 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + x = -5 + 2 Combine like terms: -2 + 2 = 0 0 + x = -5 + 2 x = -5 + 2 Combine like terms: -5 + 2 = -3 x = -3 Simplifying x = -3

Solution

The solution to the problem is based on the solutions from the subproblems. x = {7, -3}

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