c^2-3c-85=0

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Solution for c^2-3c-85=0 equation:


Simplifying
c2 + -3c + -85 = 0

Reorder the terms:
-85 + -3c + c2 = 0

Solving
-85 + -3c + c2 = 0

Solving for variable 'c'.

Begin completing the square.

Move the constant term to the right:

Add '85' to each side of the equation.
-85 + -3c + 85 + c2 = 0 + 85

Reorder the terms:
-85 + 85 + -3c + c2 = 0 + 85

Combine like terms: -85 + 85 = 0
0 + -3c + c2 = 0 + 85
-3c + c2 = 0 + 85

Combine like terms: 0 + 85 = 85
-3c + c2 = 85

The c term is -3c.  Take half its coefficient (-1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
-3c + 2.25 + c2 = 85 + 2.25

Reorder the terms:
2.25 + -3c + c2 = 85 + 2.25

Combine like terms: 85 + 2.25 = 87.25
2.25 + -3c + c2 = 87.25

Factor a perfect square on the left side:
(c + -1.5)(c + -1.5) = 87.25

Calculate the square root of the right side: 9.340770846

Break this problem into two subproblems by setting 
(c + -1.5) equal to 9.340770846 and -9.340770846.

Subproblem 1

c + -1.5 = 9.340770846 Simplifying c + -1.5 = 9.340770846 Reorder the terms: -1.5 + c = 9.340770846 Solving -1.5 + c = 9.340770846 Solving for variable 'c'. Move all terms containing c to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + c = 9.340770846 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + c = 9.340770846 + 1.5 c = 9.340770846 + 1.5 Combine like terms: 9.340770846 + 1.5 = 10.840770846 c = 10.840770846 Simplifying c = 10.840770846

Subproblem 2

c + -1.5 = -9.340770846 Simplifying c + -1.5 = -9.340770846 Reorder the terms: -1.5 + c = -9.340770846 Solving -1.5 + c = -9.340770846 Solving for variable 'c'. Move all terms containing c to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + c = -9.340770846 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + c = -9.340770846 + 1.5 c = -9.340770846 + 1.5 Combine like terms: -9.340770846 + 1.5 = -7.840770846 c = -7.840770846 Simplifying c = -7.840770846

Solution

The solution to the problem is based on the solutions from the subproblems. c = {10.840770846, -7.840770846}

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