r^2-10r-87=5

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Solution for r^2-10r-87=5 equation:


Simplifying
r2 + -10r + -87 = 5

Reorder the terms:
-87 + -10r + r2 = 5

Solving
-87 + -10r + r2 = 5

Solving for variable 'r'.

Reorder the terms:
-87 + -5 + -10r + r2 = 5 + -5

Combine like terms: -87 + -5 = -92
-92 + -10r + r2 = 5 + -5

Combine like terms: 5 + -5 = 0
-92 + -10r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '92' to each side of the equation.
-92 + -10r + 92 + r2 = 0 + 92

Reorder the terms:
-92 + 92 + -10r + r2 = 0 + 92

Combine like terms: -92 + 92 = 0
0 + -10r + r2 = 0 + 92
-10r + r2 = 0 + 92

Combine like terms: 0 + 92 = 92
-10r + r2 = 92

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 = 92 + 25

Reorder the terms:
25 + -10r + r2 = 92 + 25

Combine like terms: 92 + 25 = 117
25 + -10r + r2 = 117

Factor a perfect square on the left side:
(r + -5)(r + -5) = 117

Calculate the square root of the right side: 10.816653826

Break this problem into two subproblems by setting 
(r + -5) equal to 10.816653826 and -10.816653826.

Subproblem 1

r + -5 = 10.816653826 Simplifying r + -5 = 10.816653826 Reorder the terms: -5 + r = 10.816653826 Solving -5 + r = 10.816653826 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 = 10.816653826 + 5 Combine like terms: -5 + 5 = 0 0 + r = 10.816653826 + 5 r = 10.816653826 + 5 Combine like terms: 10.816653826 + 5 = 15.816653826 r = 15.816653826 Simplifying r = 15.816653826

Subproblem 2

r + -5 = -10.816653826 Simplifying r + -5 = -10.816653826 Reorder the terms: -5 + r = -10.816653826 Solving -5 + r = -10.816653826 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 = -10.816653826 + 5 Combine like terms: -5 + 5 = 0 0 + r = -10.816653826 + 5 r = -10.816653826 + 5 Combine like terms: -10.816653826 + 5 = -5.816653826 r = -5.816653826 Simplifying r = -5.816653826

Solution

The solution to the problem is based on the solutions from the subproblems. r = {15.816653826, -5.816653826}

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