621.72=6.28r^2+112.944r

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Solution for 621.72=6.28r^2+112.944r equation:


Simplifying
621.72 = 6.28r2 + 112.944r

Reorder the terms:
621.72 = 112.944r + 6.28r2

Solving
621.72 = 112.944r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
621.72 + -112.944r + -6.28r2 = 112.944r + -112.944r + 6.28r2 + -6.28r2

Combine like terms: 112.944r + -112.944r = 0.000
621.72 + -112.944r + -6.28r2 = 0.000 + 6.28r2 + -6.28r2
621.72 + -112.944r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
621.72 + -112.944r + -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'.
-99 + 17.98471338r + r2 = 0

Move the constant term to the right:

Add '99' to each side of the equation.
-99 + 17.98471338r + 99 + r2 = 0 + 99

Reorder the terms:
-99 + 99 + 17.98471338r + r2 = 0 + 99

Combine like terms: -99 + 99 = 0
0 + 17.98471338r + r2 = 0 + 99
17.98471338r + r2 = 0 + 99

Combine like terms: 0 + 99 = 99
17.98471338r + r2 = 99

The r term is 17.98471338r.  Take half its coefficient (8.99235669).
Square it (80.86247884) and add it to both sides.

Add '80.86247884' to each side of the equation.
17.98471338r + 80.86247884 + r2 = 99 + 80.86247884

Reorder the terms:
80.86247884 + 17.98471338r + r2 = 99 + 80.86247884

Combine like terms: 99 + 80.86247884 = 179.86247884
80.86247884 + 17.98471338r + r2 = 179.86247884

Factor a perfect square on the left side:
(r + 8.99235669)(r + 8.99235669) = 179.86247884

Calculate the square root of the right side: 13.411281775

Break this problem into two subproblems by setting 
(r + 8.99235669) equal to 13.411281775 and -13.411281775.

Subproblem 1

r + 8.99235669 = 13.411281775 Simplifying r + 8.99235669 = 13.411281775 Reorder the terms: 8.99235669 + r = 13.411281775 Solving 8.99235669 + r = 13.411281775 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-8.99235669' to each side of the equation. 8.99235669 + -8.99235669 + r = 13.411281775 + -8.99235669 Combine like terms: 8.99235669 + -8.99235669 = 0.00000000 0.00000000 + r = 13.411281775 + -8.99235669 r = 13.411281775 + -8.99235669 Combine like terms: 13.411281775 + -8.99235669 = 4.418925085 r = 4.418925085 Simplifying r = 4.418925085

Subproblem 2

r + 8.99235669 = -13.411281775 Simplifying r + 8.99235669 = -13.411281775 Reorder the terms: 8.99235669 + r = -13.411281775 Solving 8.99235669 + r = -13.411281775 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-8.99235669' to each side of the equation. 8.99235669 + -8.99235669 + r = -13.411281775 + -8.99235669 Combine like terms: 8.99235669 + -8.99235669 = 0.00000000 0.00000000 + r = -13.411281775 + -8.99235669 r = -13.411281775 + -8.99235669 Combine like terms: -13.411281775 + -8.99235669 = -22.403638465 r = -22.403638465 Simplifying r = -22.403638465

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4.418925085, -22.403638465}

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