.4x^2+1.4x=7

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Solution for .4x^2+1.4x=7 equation:


Simplifying
0.4x2 + 1.4x = 7

Reorder the terms:
1.4x + 0.4x2 = 7

Solving
1.4x + 0.4x2 = 7

Solving for variable 'x'.

Reorder the terms:
-7 + 1.4x + 0.4x2 = 7 + -7

Combine like terms: 7 + -7 = 0
-7 + 1.4x + 0.4x2 = 0

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

Divide each side by '0.4'.
-17.5 + 3.5x + x2 = 0

Move the constant term to the right:

Add '17.5' to each side of the equation.
-17.5 + 3.5x + 17.5 + x2 = 0 + 17.5

Reorder the terms:
-17.5 + 17.5 + 3.5x + x2 = 0 + 17.5

Combine like terms: -17.5 + 17.5 = 0.0
0.0 + 3.5x + x2 = 0 + 17.5
3.5x + x2 = 0 + 17.5

Combine like terms: 0 + 17.5 = 17.5
3.5x + x2 = 17.5

The x term is 3.5x.  Take half its coefficient (1.75).
Square it (3.0625) and add it to both sides.

Add '3.0625' to each side of the equation.
3.5x + 3.0625 + x2 = 17.5 + 3.0625

Reorder the terms:
3.0625 + 3.5x + x2 = 17.5 + 3.0625

Combine like terms: 17.5 + 3.0625 = 20.5625
3.0625 + 3.5x + x2 = 20.5625

Factor a perfect square on the left side:
(x + 1.75)(x + 1.75) = 20.5625

Calculate the square root of the right side: 4.534589287

Break this problem into two subproblems by setting 
(x + 1.75) equal to 4.534589287 and -4.534589287.

Subproblem 1

x + 1.75 = 4.534589287 Simplifying x + 1.75 = 4.534589287 Reorder the terms: 1.75 + x = 4.534589287 Solving 1.75 + x = 4.534589287 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.75' to each side of the equation. 1.75 + -1.75 + x = 4.534589287 + -1.75 Combine like terms: 1.75 + -1.75 = 0.00 0.00 + x = 4.534589287 + -1.75 x = 4.534589287 + -1.75 Combine like terms: 4.534589287 + -1.75 = 2.784589287 x = 2.784589287 Simplifying x = 2.784589287

Subproblem 2

x + 1.75 = -4.534589287 Simplifying x + 1.75 = -4.534589287 Reorder the terms: 1.75 + x = -4.534589287 Solving 1.75 + x = -4.534589287 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.75' to each side of the equation. 1.75 + -1.75 + x = -4.534589287 + -1.75 Combine like terms: 1.75 + -1.75 = 0.00 0.00 + x = -4.534589287 + -1.75 x = -4.534589287 + -1.75 Combine like terms: -4.534589287 + -1.75 = -6.284589287 x = -6.284589287 Simplifying x = -6.284589287

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.784589287, -6.284589287}

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