81650.99=2*3.14*r^2+2*3.14*r*287.8

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Solution for 81650.99=2*3.14*r^2+2*3.14*r*287.8 equation:


Simplifying
81650.99 = 2 * 3.14r2 + 2 * 3.14r * 287.8

Multiply 2 * 3.14
81650.99 = 6.28r2 + 2 * 3.14r * 287.8

Reorder the terms for easier multiplication:
81650.99 = 6.28r2 + 2 * 3.14 * 287.8r

Multiply 2 * 3.14
81650.99 = 6.28r2 + 6.28 * 287.8r

Multiply 6.28 * 287.8
81650.99 = 6.28r2 + 1807.384r

Reorder the terms:
81650.99 = 1807.384r + 6.28r2

Solving
81650.99 = 1807.384r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
81650.99 + -1807.384r + -6.28r2 = 1807.384r + -1807.384r + 6.28r2 + -6.28r2

Combine like terms: 1807.384r + -1807.384r = 0.000
81650.99 + -1807.384r + -6.28r2 = 0.000 + 6.28r2 + -6.28r2
81650.99 + -1807.384r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
81650.99 + -1807.384r + -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'.
-13001.75 + 287.8r + r2 = 0

Move the constant term to the right:

Add '13001.75' to each side of the equation.
-13001.75 + 287.8r + 13001.75 + r2 = 0 + 13001.75

Reorder the terms:
-13001.75 + 13001.75 + 287.8r + r2 = 0 + 13001.75

Combine like terms: -13001.75 + 13001.75 = 0.00
0.00 + 287.8r + r2 = 0 + 13001.75
287.8r + r2 = 0 + 13001.75

Combine like terms: 0 + 13001.75 = 13001.75
287.8r + r2 = 13001.75

The r term is 287.8r.  Take half its coefficient (143.9).
Square it (20707.21) and add it to both sides.

Add '20707.21' to each side of the equation.
287.8r + 20707.21 + r2 = 13001.75 + 20707.21

Reorder the terms:
20707.21 + 287.8r + r2 = 13001.75 + 20707.21

Combine like terms: 13001.75 + 20707.21 = 33708.96
20707.21 + 287.8r + r2 = 33708.96

Factor a perfect square on the left side:
(r + 143.9)(r + 143.9) = 33708.96

Calculate the square root of the right side: 183.6

Break this problem into two subproblems by setting 
(r + 143.9) equal to 183.6 and -183.6.

Subproblem 1

r + 143.9 = 183.6 Simplifying r + 143.9 = 183.6 Reorder the terms: 143.9 + r = 183.6 Solving 143.9 + r = 183.6 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-143.9' to each side of the equation. 143.9 + -143.9 + r = 183.6 + -143.9 Combine like terms: 143.9 + -143.9 = 0.0 0.0 + r = 183.6 + -143.9 r = 183.6 + -143.9 Combine like terms: 183.6 + -143.9 = 39.7 r = 39.7 Simplifying r = 39.7

Subproblem 2

r + 143.9 = -183.6 Simplifying r + 143.9 = -183.6 Reorder the terms: 143.9 + r = -183.6 Solving 143.9 + r = -183.6 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-143.9' to each side of the equation. 143.9 + -143.9 + r = -183.6 + -143.9 Combine like terms: 143.9 + -143.9 = 0.0 0.0 + r = -183.6 + -143.9 r = -183.6 + -143.9 Combine like terms: -183.6 + -143.9 = -327.5 r = -327.5 Simplifying r = -327.5

Solution

The solution to the problem is based on the solutions from the subproblems. r = {39.7, -327.5}

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