r^2-10r-99=0

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Solution for r^2-10r-99=0 equation:


Simplifying
r2 + -10r + -99 = 0

Reorder the terms:
-99 + -10r + r2 = 0

Solving
-99 + -10r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '99' to each side of the equation.
-99 + -10r + 99 + r2 = 0 + 99

Reorder the terms:
-99 + 99 + -10r + r2 = 0 + 99

Combine like terms: -99 + 99 = 0
0 + -10r + r2 = 0 + 99
-10r + r2 = 0 + 99

Combine like terms: 0 + 99 = 99
-10r + r2 = 99

The r term is -10r.  Take half its coefficient (-5).
Square it (25) and add it to both sides.

Add '25' to each side of the equation.
-10r + 25 + r2 = 99 + 25

Reorder the terms:
25 + -10r + r2 = 99 + 25

Combine like terms: 99 + 25 = 124
25 + -10r + r2 = 124

Factor a perfect square on the left side:
(r + -5)(r + -5) = 124

Calculate the square root of the right side: 11.135528726

Break this problem into two subproblems by setting 
(r + -5) equal to 11.135528726 and -11.135528726.

Subproblem 1

r + -5 = 11.135528726 Simplifying r + -5 = 11.135528726 Reorder the terms: -5 + r = 11.135528726 Solving -5 + r = 11.135528726 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '5' to each side of the equation. -5 + 5 + r = 11.135528726 + 5 Combine like terms: -5 + 5 = 0 0 + r = 11.135528726 + 5 r = 11.135528726 + 5 Combine like terms: 11.135528726 + 5 = 16.135528726 r = 16.135528726 Simplifying r = 16.135528726

Subproblem 2

r + -5 = -11.135528726 Simplifying r + -5 = -11.135528726 Reorder the terms: -5 + r = -11.135528726 Solving -5 + r = -11.135528726 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '5' to each side of the equation. -5 + 5 + r = -11.135528726 + 5 Combine like terms: -5 + 5 = 0 0 + r = -11.135528726 + 5 r = -11.135528726 + 5 Combine like terms: -11.135528726 + 5 = -6.135528726 r = -6.135528726 Simplifying r = -6.135528726

Solution

The solution to the problem is based on the solutions from the subproblems. r = {16.135528726, -6.135528726}

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