n(n-1)=80

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Solution for n(n-1)=80 equation:


Simplifying
n(n + -1) = 80

Reorder the terms:
n(-1 + n) = 80
(-1 * n + n * n) = 80
(-1n + n2) = 80

Solving
-1n + n2 = 80

Solving for variable 'n'.

Reorder the terms:
-80 + -1n + n2 = 80 + -80

Combine like terms: 80 + -80 = 0
-80 + -1n + n2 = 0

Begin completing the square.

Move the constant term to the right:

Add '80' to each side of the equation.
-80 + -1n + 80 + n2 = 0 + 80

Reorder the terms:
-80 + 80 + -1n + n2 = 0 + 80

Combine like terms: -80 + 80 = 0
0 + -1n + n2 = 0 + 80
-1n + n2 = 0 + 80

Combine like terms: 0 + 80 = 80
-1n + n2 = 80

The n term is -1n.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1n + 0.25 + n2 = 80 + 0.25

Reorder the terms:
0.25 + -1n + n2 = 80 + 0.25

Combine like terms: 80 + 0.25 = 80.25
0.25 + -1n + n2 = 80.25

Factor a perfect square on the left side:
(n + -0.5)(n + -0.5) = 80.25

Calculate the square root of the right side: 8.958236434

Break this problem into two subproblems by setting 
(n + -0.5) equal to 8.958236434 and -8.958236434.

Subproblem 1

n + -0.5 = 8.958236434 Simplifying n + -0.5 = 8.958236434 Reorder the terms: -0.5 + n = 8.958236434 Solving -0.5 + n = 8.958236434 Solving for variable 'n'. Move all terms containing n to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + n = 8.958236434 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + n = 8.958236434 + 0.5 n = 8.958236434 + 0.5 Combine like terms: 8.958236434 + 0.5 = 9.458236434 n = 9.458236434 Simplifying n = 9.458236434

Subproblem 2

n + -0.5 = -8.958236434 Simplifying n + -0.5 = -8.958236434 Reorder the terms: -0.5 + n = -8.958236434 Solving -0.5 + n = -8.958236434 Solving for variable 'n'. Move all terms containing n to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + n = -8.958236434 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + n = -8.958236434 + 0.5 n = -8.958236434 + 0.5 Combine like terms: -8.958236434 + 0.5 = -8.458236434 n = -8.458236434 Simplifying n = -8.458236434

Solution

The solution to the problem is based on the solutions from the subproblems. n = {9.458236434, -8.458236434}

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