15=4.3n-2.1n(n-4)

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Solution for 15=4.3n-2.1n(n-4) equation:


Simplifying
15 = 4.3n + -2.1n(n + -4)

Reorder the terms:
15 = 4.3n + -2.1n(-4 + n)
15 = 4.3n + (-4 * -2.1n + n * -2.1n)
15 = 4.3n + (8.4n + -2.1n2)

Combine like terms: 4.3n + 8.4n = 12.7n
15 = 12.7n + -2.1n2

Solving
15 = 12.7n + -2.1n2

Solving for variable 'n'.

Reorder the terms:
15 + -12.7n + 2.1n2 = 12.7n + -12.7n + -2.1n2 + 2.1n2

Combine like terms: 12.7n + -12.7n = 0.0
15 + -12.7n + 2.1n2 = 0.0 + -2.1n2 + 2.1n2
15 + -12.7n + 2.1n2 = -2.1n2 + 2.1n2

Combine like terms: -2.1n2 + 2.1n2 = 0.0
15 + -12.7n + 2.1n2 = 0.0

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

Divide each side by '2.1'.
7.142857143 + -6.047619048n + n2 = 0

Move the constant term to the right:

Add '-7.142857143' to each side of the equation.
7.142857143 + -6.047619048n + -7.142857143 + n2 = 0 + -7.142857143

Reorder the terms:
7.142857143 + -7.142857143 + -6.047619048n + n2 = 0 + -7.142857143

Combine like terms: 7.142857143 + -7.142857143 = 0.000000000
0.000000000 + -6.047619048n + n2 = 0 + -7.142857143
-6.047619048n + n2 = 0 + -7.142857143

Combine like terms: 0 + -7.142857143 = -7.142857143
-6.047619048n + n2 = -7.142857143

The n term is -6.047619048n.  Take half its coefficient (-3.023809524).
Square it (9.143424037) and add it to both sides.

Add '9.143424037' to each side of the equation.
-6.047619048n + 9.143424037 + n2 = -7.142857143 + 9.143424037

Reorder the terms:
9.143424037 + -6.047619048n + n2 = -7.142857143 + 9.143424037

Combine like terms: -7.142857143 + 9.143424037 = 2.000566894
9.143424037 + -6.047619048n + n2 = 2.000566894

Factor a perfect square on the left side:
(n + -3.023809524)(n + -3.023809524) = 2.000566894

Calculate the square root of the right side: 1.414413975

Break this problem into two subproblems by setting 
(n + -3.023809524) equal to 1.414413975 and -1.414413975.

Subproblem 1

n + -3.023809524 = 1.414413975 Simplifying n + -3.023809524 = 1.414413975 Reorder the terms: -3.023809524 + n = 1.414413975 Solving -3.023809524 + n = 1.414413975 Solving for variable 'n'. Move all terms containing n to the left, all other terms to the right. Add '3.023809524' to each side of the equation. -3.023809524 + 3.023809524 + n = 1.414413975 + 3.023809524 Combine like terms: -3.023809524 + 3.023809524 = 0.000000000 0.000000000 + n = 1.414413975 + 3.023809524 n = 1.414413975 + 3.023809524 Combine like terms: 1.414413975 + 3.023809524 = 4.438223499 n = 4.438223499 Simplifying n = 4.438223499

Subproblem 2

n + -3.023809524 = -1.414413975 Simplifying n + -3.023809524 = -1.414413975 Reorder the terms: -3.023809524 + n = -1.414413975 Solving -3.023809524 + n = -1.414413975 Solving for variable 'n'. Move all terms containing n to the left, all other terms to the right. Add '3.023809524' to each side of the equation. -3.023809524 + 3.023809524 + n = -1.414413975 + 3.023809524 Combine like terms: -3.023809524 + 3.023809524 = 0.000000000 0.000000000 + n = -1.414413975 + 3.023809524 n = -1.414413975 + 3.023809524 Combine like terms: -1.414413975 + 3.023809524 = 1.609395549 n = 1.609395549 Simplifying n = 1.609395549

Solution

The solution to the problem is based on the solutions from the subproblems. n = {4.438223499, 1.609395549}

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