r^2+r-18=0

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Solution for r^2+r-18=0 equation:


Simplifying
r2 + r + -18 = 0

Reorder the terms:
-18 + r + r2 = 0

Solving
-18 + r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '18' to each side of the equation.
-18 + r + 18 + r2 = 0 + 18

Reorder the terms:
-18 + 18 + r + r2 = 0 + 18

Combine like terms: -18 + 18 = 0
0 + r + r2 = 0 + 18
r + r2 = 0 + 18

Combine like terms: 0 + 18 = 18
r + r2 = 18

The r term is r.  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.
r + 0.25 + r2 = 18 + 0.25

Reorder the terms:
0.25 + r + r2 = 18 + 0.25

Combine like terms: 18 + 0.25 = 18.25
0.25 + r + r2 = 18.25

Factor a perfect square on the left side:
(r + 0.5)(r + 0.5) = 18.25

Calculate the square root of the right side: 4.272001873

Break this problem into two subproblems by setting 
(r + 0.5) equal to 4.272001873 and -4.272001873.

Subproblem 1

r + 0.5 = 4.272001873 Simplifying r + 0.5 = 4.272001873 Reorder the terms: 0.5 + r = 4.272001873 Solving 0.5 + r = 4.272001873 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + r = 4.272001873 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + r = 4.272001873 + -0.5 r = 4.272001873 + -0.5 Combine like terms: 4.272001873 + -0.5 = 3.772001873 r = 3.772001873 Simplifying r = 3.772001873

Subproblem 2

r + 0.5 = -4.272001873 Simplifying r + 0.5 = -4.272001873 Reorder the terms: 0.5 + r = -4.272001873 Solving 0.5 + r = -4.272001873 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + r = -4.272001873 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + r = -4.272001873 + -0.5 r = -4.272001873 + -0.5 Combine like terms: -4.272001873 + -0.5 = -4.772001873 r = -4.772001873 Simplifying r = -4.772001873

Solution

The solution to the problem is based on the solutions from the subproblems. r = {3.772001873, -4.772001873}

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