15=7x^2-4x

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Solution for 15=7x^2-4x equation:


Simplifying
15 = 7x2 + -4x

Reorder the terms:
15 = -4x + 7x2

Solving
15 = -4x + 7x2

Solving for variable 'x'.

Reorder the terms:
15 + 4x + -7x2 = -4x + 4x + 7x2 + -7x2

Combine like terms: -4x + 4x = 0
15 + 4x + -7x2 = 0 + 7x2 + -7x2
15 + 4x + -7x2 = 7x2 + -7x2

Combine like terms: 7x2 + -7x2 = 0
15 + 4x + -7x2 = 0

Begin completing the square.  Divide all terms by
-7 the coefficient of the squared term: 

Divide each side by '-7'.
-2.142857143 + -0.5714285714x + x2 = 0

Move the constant term to the right:

Add '2.142857143' to each side of the equation.
-2.142857143 + -0.5714285714x + 2.142857143 + x2 = 0 + 2.142857143

Reorder the terms:
-2.142857143 + 2.142857143 + -0.5714285714x + x2 = 0 + 2.142857143

Combine like terms: -2.142857143 + 2.142857143 = 0.000000000
0.000000000 + -0.5714285714x + x2 = 0 + 2.142857143
-0.5714285714x + x2 = 0 + 2.142857143

Combine like terms: 0 + 2.142857143 = 2.142857143
-0.5714285714x + x2 = 2.142857143

The x term is -0.5714285714x.  Take half its coefficient (-0.2857142857).
Square it (0.08163265305) and add it to both sides.

Add '0.08163265305' to each side of the equation.
-0.5714285714x + 0.08163265305 + x2 = 2.142857143 + 0.08163265305

Reorder the terms:
0.08163265305 + -0.5714285714x + x2 = 2.142857143 + 0.08163265305

Combine like terms: 2.142857143 + 0.08163265305 = 2.22448979605
0.08163265305 + -0.5714285714x + x2 = 2.22448979605

Factor a perfect square on the left side:
(x + -0.2857142857)(x + -0.2857142857) = 2.22448979605

Calculate the square root of the right side: 1.491472358

Break this problem into two subproblems by setting 
(x + -0.2857142857) equal to 1.491472358 and -1.491472358.

Subproblem 1

x + -0.2857142857 = 1.491472358 Simplifying x + -0.2857142857 = 1.491472358 Reorder the terms: -0.2857142857 + x = 1.491472358 Solving -0.2857142857 + x = 1.491472358 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.2857142857' to each side of the equation. -0.2857142857 + 0.2857142857 + x = 1.491472358 + 0.2857142857 Combine like terms: -0.2857142857 + 0.2857142857 = 0.0000000000 0.0000000000 + x = 1.491472358 + 0.2857142857 x = 1.491472358 + 0.2857142857 Combine like terms: 1.491472358 + 0.2857142857 = 1.7771866437 x = 1.7771866437 Simplifying x = 1.7771866437

Subproblem 2

x + -0.2857142857 = -1.491472358 Simplifying x + -0.2857142857 = -1.491472358 Reorder the terms: -0.2857142857 + x = -1.491472358 Solving -0.2857142857 + x = -1.491472358 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.2857142857' to each side of the equation. -0.2857142857 + 0.2857142857 + x = -1.491472358 + 0.2857142857 Combine like terms: -0.2857142857 + 0.2857142857 = 0.0000000000 0.0000000000 + x = -1.491472358 + 0.2857142857 x = -1.491472358 + 0.2857142857 Combine like terms: -1.491472358 + 0.2857142857 = -1.2057580723 x = -1.2057580723 Simplifying x = -1.2057580723

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.7771866437, -1.2057580723}

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