f^2+18f-31=0

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Solution for f^2+18f-31=0 equation:


Simplifying
f2 + 18f + -31 = 0

Reorder the terms:
-31 + 18f + f2 = 0

Solving
-31 + 18f + f2 = 0

Solving for variable 'f'.

Begin completing the square.

Move the constant term to the right:

Add '31' to each side of the equation.
-31 + 18f + 31 + f2 = 0 + 31

Reorder the terms:
-31 + 31 + 18f + f2 = 0 + 31

Combine like terms: -31 + 31 = 0
0 + 18f + f2 = 0 + 31
18f + f2 = 0 + 31

Combine like terms: 0 + 31 = 31
18f + f2 = 31

The f term is 18f.  Take half its coefficient (9).
Square it (81) and add it to both sides.

Add '81' to each side of the equation.
18f + 81 + f2 = 31 + 81

Reorder the terms:
81 + 18f + f2 = 31 + 81

Combine like terms: 31 + 81 = 112
81 + 18f + f2 = 112

Factor a perfect square on the left side:
(f + 9)(f + 9) = 112

Calculate the square root of the right side: 10.583005244

Break this problem into two subproblems by setting 
(f + 9) equal to 10.583005244 and -10.583005244.

Subproblem 1

f + 9 = 10.583005244 Simplifying f + 9 = 10.583005244 Reorder the terms: 9 + f = 10.583005244 Solving 9 + f = 10.583005244 Solving for variable 'f'. Move all terms containing f to the left, all other terms to the right. Add '-9' to each side of the equation. 9 + -9 + f = 10.583005244 + -9 Combine like terms: 9 + -9 = 0 0 + f = 10.583005244 + -9 f = 10.583005244 + -9 Combine like terms: 10.583005244 + -9 = 1.583005244 f = 1.583005244 Simplifying f = 1.583005244

Subproblem 2

f + 9 = -10.583005244 Simplifying f + 9 = -10.583005244 Reorder the terms: 9 + f = -10.583005244 Solving 9 + f = -10.583005244 Solving for variable 'f'. Move all terms containing f to the left, all other terms to the right. Add '-9' to each side of the equation. 9 + -9 + f = -10.583005244 + -9 Combine like terms: 9 + -9 = 0 0 + f = -10.583005244 + -9 f = -10.583005244 + -9 Combine like terms: -10.583005244 + -9 = -19.583005244 f = -19.583005244 Simplifying f = -19.583005244

Solution

The solution to the problem is based on the solutions from the subproblems. f = {1.583005244, -19.583005244}

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