r^2-18r=13

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Solution for r^2-18r=13 equation:


Simplifying
r2 + -18r = 13

Reorder the terms:
-18r + r2 = 13

Solving
-18r + r2 = 13

Solving for variable 'r'.

Reorder the terms:
-13 + -18r + r2 = 13 + -13

Combine like terms: 13 + -13 = 0
-13 + -18r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '13' to each side of the equation.
-13 + -18r + 13 + r2 = 0 + 13

Reorder the terms:
-13 + 13 + -18r + r2 = 0 + 13

Combine like terms: -13 + 13 = 0
0 + -18r + r2 = 0 + 13
-18r + r2 = 0 + 13

Combine like terms: 0 + 13 = 13
-18r + r2 = 13

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 = 13 + 81

Reorder the terms:
81 + -18r + r2 = 13 + 81

Combine like terms: 13 + 81 = 94
81 + -18r + r2 = 94

Factor a perfect square on the left side:
(r + -9)(r + -9) = 94

Calculate the square root of the right side: 9.695359715

Break this problem into two subproblems by setting 
(r + -9) equal to 9.695359715 and -9.695359715.

Subproblem 1

r + -9 = 9.695359715 Simplifying r + -9 = 9.695359715 Reorder the terms: -9 + r = 9.695359715 Solving -9 + r = 9.695359715 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 = 9.695359715 + 9 Combine like terms: -9 + 9 = 0 0 + r = 9.695359715 + 9 r = 9.695359715 + 9 Combine like terms: 9.695359715 + 9 = 18.695359715 r = 18.695359715 Simplifying r = 18.695359715

Subproblem 2

r + -9 = -9.695359715 Simplifying r + -9 = -9.695359715 Reorder the terms: -9 + r = -9.695359715 Solving -9 + r = -9.695359715 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 = -9.695359715 + 9 Combine like terms: -9 + 9 = 0 0 + r = -9.695359715 + 9 r = -9.695359715 + 9 Combine like terms: -9.695359715 + 9 = -0.695359715 r = -0.695359715 Simplifying r = -0.695359715

Solution

The solution to the problem is based on the solutions from the subproblems. r = {18.695359715, -0.695359715}

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