r^2-r-4=0

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


Simplifying
r2 + -1r + -4 = 0

Reorder the terms:
-4 + -1r + r2 = 0

Solving
-4 + -1r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '4' to each side of the equation.
-4 + -1r + 4 + r2 = 0 + 4

Reorder the terms:
-4 + 4 + -1r + r2 = 0 + 4

Combine like terms: -4 + 4 = 0
0 + -1r + r2 = 0 + 4
-1r + r2 = 0 + 4

Combine like terms: 0 + 4 = 4
-1r + r2 = 4

The r term is -1r.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1r + 0.25 + r2 = 4 + 0.25

Reorder the terms:
0.25 + -1r + r2 = 4 + 0.25

Combine like terms: 4 + 0.25 = 4.25
0.25 + -1r + r2 = 4.25

Factor a perfect square on the left side:
(r + -0.5)(r + -0.5) = 4.25

Calculate the square root of the right side: 2.061552813

Break this problem into two subproblems by setting 
(r + -0.5) equal to 2.061552813 and -2.061552813.

Subproblem 1

r + -0.5 = 2.061552813 Simplifying r + -0.5 = 2.061552813 Reorder the terms: -0.5 + r = 2.061552813 Solving -0.5 + r = 2.061552813 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = 2.061552813 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = 2.061552813 + 0.5 r = 2.061552813 + 0.5 Combine like terms: 2.061552813 + 0.5 = 2.561552813 r = 2.561552813 Simplifying r = 2.561552813

Subproblem 2

r + -0.5 = -2.061552813 Simplifying r + -0.5 = -2.061552813 Reorder the terms: -0.5 + r = -2.061552813 Solving -0.5 + r = -2.061552813 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = -2.061552813 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = -2.061552813 + 0.5 r = -2.061552813 + 0.5 Combine like terms: -2.061552813 + 0.5 = -1.561552813 r = -1.561552813 Simplifying r = -1.561552813

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.561552813, -1.561552813}

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