r*r+4r-16=0

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Solution for r*r+4r-16=0 equation:


Simplifying
r * r + 4r + -16 = 0

Multiply r * r
r2 + 4r + -16 = 0

Reorder the terms:
-16 + 4r + r2 = 0

Solving
-16 + 4r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '16' to each side of the equation.
-16 + 4r + 16 + r2 = 0 + 16

Reorder the terms:
-16 + 16 + 4r + r2 = 0 + 16

Combine like terms: -16 + 16 = 0
0 + 4r + r2 = 0 + 16
4r + r2 = 0 + 16

Combine like terms: 0 + 16 = 16
4r + r2 = 16

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 = 16 + 4

Reorder the terms:
4 + 4r + r2 = 16 + 4

Combine like terms: 16 + 4 = 20
4 + 4r + r2 = 20

Factor a perfect square on the left side:
(r + 2)(r + 2) = 20

Calculate the square root of the right side: 4.472135955

Break this problem into two subproblems by setting 
(r + 2) equal to 4.472135955 and -4.472135955.

Subproblem 1

r + 2 = 4.472135955 Simplifying r + 2 = 4.472135955 Reorder the terms: 2 + r = 4.472135955 Solving 2 + r = 4.472135955 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 = 4.472135955 + -2 Combine like terms: 2 + -2 = 0 0 + r = 4.472135955 + -2 r = 4.472135955 + -2 Combine like terms: 4.472135955 + -2 = 2.472135955 r = 2.472135955 Simplifying r = 2.472135955

Subproblem 2

r + 2 = -4.472135955 Simplifying r + 2 = -4.472135955 Reorder the terms: 2 + r = -4.472135955 Solving 2 + r = -4.472135955 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 = -4.472135955 + -2 Combine like terms: 2 + -2 = 0 0 + r = -4.472135955 + -2 r = -4.472135955 + -2 Combine like terms: -4.472135955 + -2 = -6.472135955 r = -6.472135955 Simplifying r = -6.472135955

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.472135955, -6.472135955}

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