16616.88=3.14*r^2+2*3.14*r*105

Solution for 16616.88=3.14*r^2+2*3.14*r*105 equation:

Simplifying
16616.88 = 3.14r2 + 2 * 3.14r * 105

Reorder the terms for easier multiplication:
16616.88 = 3.14r2 + 2 * 3.14 * 105r

Multiply 2 * 3.14
16616.88 = 3.14r2 + 6.28 * 105r

Multiply 6.28 * 105
16616.88 = 3.14r2 + 659.4r

Reorder the terms:
16616.88 = 659.4r + 3.14r2

Solving
16616.88 = 659.4r + 3.14r2

Solving for variable 'r'.

Reorder the terms:
16616.88 + -659.4r + -3.14r2 = 659.4r + -659.4r + 3.14r2 + -3.14r2

Combine like terms: 659.4r + -659.4r = 0.0
16616.88 + -659.4r + -3.14r2 = 0.0 + 3.14r2 + -3.14r2
16616.88 + -659.4r + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
16616.88 + -659.4r + -3.14r2 = 0.00

Begin completing the square.  Divide all terms by
-3.14 the coefficient of the squared term: 

Divide each side by '-3.14'.
-5292 + 210r + r2 = 0

Move the constant term to the right:

Add '5292' to each side of the equation.
-5292 + 210r + 5292 + r2 = 0 + 5292

Reorder the terms:
-5292 + 5292 + 210r + r2 = 0 + 5292

Combine like terms: -5292 + 5292 = 0
0 + 210r + r2 = 0 + 5292
210r + r2 = 0 + 5292

Combine like terms: 0 + 5292 = 5292
210r + r2 = 5292

The r term is 210r.  Take half its coefficient (105).
Square it (11025) and add it to both sides.

Add '11025' to each side of the equation.
210r + 11025 + r2 = 5292 + 11025

Reorder the terms:
11025 + 210r + r2 = 5292 + 11025

Combine like terms: 5292 + 11025 = 16317
11025 + 210r + r2 = 16317

Factor a perfect square on the left side:
(r + 105)(r + 105) = 16317

Calculate the square root of the right side: 127.738013136

Break this problem into two subproblems by setting 
(r + 105) equal to 127.738013136 and -127.738013136.

Subproblem 1
r + 105 = 127.738013136

Simplifying
r + 105 = 127.738013136

Reorder the terms:
105 + r = 127.738013136

Solving
105 + r = 127.738013136

Solving for variable 'r'.

Move all terms containing r to the left, all other terms to the right.

Add '-105' to each side of the equation.
105 + -105 + r = 127.738013136 + -105

Combine like terms: 105 + -105 = 0
0 + r = 127.738013136 + -105
r = 127.738013136 + -105

Combine like terms: 127.738013136 + -105 = 22.738013136
r = 22.738013136

Simplifying
r = 22.738013136

Subproblem 2
r + 105 = -127.738013136

Simplifying
r + 105 = -127.738013136

Reorder the terms:
105 + r = -127.738013136

Solving
105 + r = -127.738013136

Solving for variable 'r'.

Move all terms containing r to the left, all other terms to the right.

Add '-105' to each side of the equation.
105 + -105 + r = -127.738013136 + -105

Combine like terms: 105 + -105 = 0
0 + r = -127.738013136 + -105
r = -127.738013136 + -105

Combine like terms: -127.738013136 + -105 = -232.738013136
r = -232.738013136

Simplifying
r = -232.738013136

Solution
The solution to the problem is based on the solutions
from the subproblems.
r = {22.738013136, -232.738013136}