12=6.28r(r+5)

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Solution for 12=6.28r(r+5) equation:


Simplifying
12 = 6.28r(r + 5)

Reorder the terms:
12 = 6.28r(5 + r)
12 = (5 * 6.28r + r * 6.28r)
12 = (31.4r + 6.28r2)

Solving
12 = 31.4r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
12 + -31.4r + -6.28r2 = 31.4r + -31.4r + 6.28r2 + -6.28r2

Combine like terms: 31.4r + -31.4r = 0.0
12 + -31.4r + -6.28r2 = 0.0 + 6.28r2 + -6.28r2
12 + -31.4r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
12 + -31.4r + -6.28r2 = 0.00

Begin completing the square.  Divide all terms by
-6.28 the coefficient of the squared term: 

Divide each side by '-6.28'.
-1.910828025 + 5r + r2 = 0

Move the constant term to the right:

Add '1.910828025' to each side of the equation.
-1.910828025 + 5r + 1.910828025 + r2 = 0 + 1.910828025

Reorder the terms:
-1.910828025 + 1.910828025 + 5r + r2 = 0 + 1.910828025

Combine like terms: -1.910828025 + 1.910828025 = 0.000000000
0.000000000 + 5r + r2 = 0 + 1.910828025
5r + r2 = 0 + 1.910828025

Combine like terms: 0 + 1.910828025 = 1.910828025
5r + r2 = 1.910828025

The r term is 5r.  Take half its coefficient (2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
5r + 6.25 + r2 = 1.910828025 + 6.25

Reorder the terms:
6.25 + 5r + r2 = 1.910828025 + 6.25

Combine like terms: 1.910828025 + 6.25 = 8.160828025
6.25 + 5r + r2 = 8.160828025

Factor a perfect square on the left side:
(r + 2.5)(r + 2.5) = 8.160828025

Calculate the square root of the right side: 2.856716301

Break this problem into two subproblems by setting 
(r + 2.5) equal to 2.856716301 and -2.856716301.

Subproblem 1

r + 2.5 = 2.856716301 Simplifying r + 2.5 = 2.856716301 Reorder the terms: 2.5 + r = 2.856716301 Solving 2.5 + r = 2.856716301 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + r = 2.856716301 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + r = 2.856716301 + -2.5 r = 2.856716301 + -2.5 Combine like terms: 2.856716301 + -2.5 = 0.356716301 r = 0.356716301 Simplifying r = 0.356716301

Subproblem 2

r + 2.5 = -2.856716301 Simplifying r + 2.5 = -2.856716301 Reorder the terms: 2.5 + r = -2.856716301 Solving 2.5 + r = -2.856716301 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + r = -2.856716301 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + r = -2.856716301 + -2.5 r = -2.856716301 + -2.5 Combine like terms: -2.856716301 + -2.5 = -5.356716301 r = -5.356716301 Simplifying r = -5.356716301

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.356716301, -5.356716301}

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