r^2-4r-79=0

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Solution for r^2-4r-79=0 equation:


Simplifying
r2 + -4r + -79 = 0

Reorder the terms:
-79 + -4r + r2 = 0

Solving
-79 + -4r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '79' to each side of the equation.
-79 + -4r + 79 + r2 = 0 + 79

Reorder the terms:
-79 + 79 + -4r + r2 = 0 + 79

Combine like terms: -79 + 79 = 0
0 + -4r + r2 = 0 + 79
-4r + r2 = 0 + 79

Combine like terms: 0 + 79 = 79
-4r + r2 = 79

The r term is -4r.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4r + 4 + r2 = 79 + 4

Reorder the terms:
4 + -4r + r2 = 79 + 4

Combine like terms: 79 + 4 = 83
4 + -4r + r2 = 83

Factor a perfect square on the left side:
(r + -2)(r + -2) = 83

Calculate the square root of the right side: 9.110433579

Break this problem into two subproblems by setting 
(r + -2) equal to 9.110433579 and -9.110433579.

Subproblem 1

r + -2 = 9.110433579 Simplifying r + -2 = 9.110433579 Reorder the terms: -2 + r = 9.110433579 Solving -2 + r = 9.110433579 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + r = 9.110433579 + 2 Combine like terms: -2 + 2 = 0 0 + r = 9.110433579 + 2 r = 9.110433579 + 2 Combine like terms: 9.110433579 + 2 = 11.110433579 r = 11.110433579 Simplifying r = 11.110433579

Subproblem 2

r + -2 = -9.110433579 Simplifying r + -2 = -9.110433579 Reorder the terms: -2 + r = -9.110433579 Solving -2 + r = -9.110433579 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + r = -9.110433579 + 2 Combine like terms: -2 + 2 = 0 0 + r = -9.110433579 + 2 r = -9.110433579 + 2 Combine like terms: -9.110433579 + 2 = -7.110433579 r = -7.110433579 Simplifying r = -7.110433579

Solution

The solution to the problem is based on the solutions from the subproblems. r = {11.110433579, -7.110433579}

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