r^2-18r-56=0

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Solution for r^2-18r-56=0 equation:


Simplifying
r2 + -18r + -56 = 0

Reorder the terms:
-56 + -18r + r2 = 0

Solving
-56 + -18r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '56' to each side of the equation.
-56 + -18r + 56 + r2 = 0 + 56

Reorder the terms:
-56 + 56 + -18r + r2 = 0 + 56

Combine like terms: -56 + 56 = 0
0 + -18r + r2 = 0 + 56
-18r + r2 = 0 + 56

Combine like terms: 0 + 56 = 56
-18r + r2 = 56

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

Add '81' to each side of the equation.
-18r + 81 + r2 = 56 + 81

Reorder the terms:
81 + -18r + r2 = 56 + 81

Combine like terms: 56 + 81 = 137
81 + -18r + r2 = 137

Factor a perfect square on the left side:
(r + -9)(r + -9) = 137

Calculate the square root of the right side: 11.704699911

Break this problem into two subproblems by setting 
(r + -9) equal to 11.704699911 and -11.704699911.

Subproblem 1

r + -9 = 11.704699911 Simplifying r + -9 = 11.704699911 Reorder the terms: -9 + r = 11.704699911 Solving -9 + r = 11.704699911 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '9' to each side of the equation. -9 + 9 + r = 11.704699911 + 9 Combine like terms: -9 + 9 = 0 0 + r = 11.704699911 + 9 r = 11.704699911 + 9 Combine like terms: 11.704699911 + 9 = 20.704699911 r = 20.704699911 Simplifying r = 20.704699911

Subproblem 2

r + -9 = -11.704699911 Simplifying r + -9 = -11.704699911 Reorder the terms: -9 + r = -11.704699911 Solving -9 + r = -11.704699911 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '9' to each side of the equation. -9 + 9 + r = -11.704699911 + 9 Combine like terms: -9 + 9 = 0 0 + r = -11.704699911 + 9 r = -11.704699911 + 9 Combine like terms: -11.704699911 + 9 = -2.704699911 r = -2.704699911 Simplifying r = -2.704699911

Solution

The solution to the problem is based on the solutions from the subproblems. r = {20.704699911, -2.704699911}

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