200.96=2*3.14*r^2+2*3.14*r*4

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Solution for 200.96=2*3.14*r^2+2*3.14*r*4 equation:


Simplifying
200.96 = 2 * 3.14r2 + 2 * 3.14r * 4

Multiply 2 * 3.14
200.96 = 6.28r2 + 2 * 3.14r * 4

Reorder the terms for easier multiplication:
200.96 = 6.28r2 + 2 * 3.14 * 4r

Multiply 2 * 3.14
200.96 = 6.28r2 + 6.28 * 4r

Multiply 6.28 * 4
200.96 = 6.28r2 + 25.12r

Reorder the terms:
200.96 = 25.12r + 6.28r2

Solving
200.96 = 25.12r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
200.96 + -25.12r + -6.28r2 = 25.12r + -25.12r + 6.28r2 + -6.28r2

Combine like terms: 25.12r + -25.12r = 0.00
200.96 + -25.12r + -6.28r2 = 0.00 + 6.28r2 + -6.28r2
200.96 + -25.12r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
200.96 + -25.12r + -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'.
-32 + 4r + r2 = 0

Move the constant term to the right:

Add '32' to each side of the equation.
-32 + 4r + 32 + r2 = 0 + 32

Reorder the terms:
-32 + 32 + 4r + r2 = 0 + 32

Combine like terms: -32 + 32 = 0
0 + 4r + r2 = 0 + 32
4r + r2 = 0 + 32

Combine like terms: 0 + 32 = 32
4r + r2 = 32

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 = 32 + 4

Reorder the terms:
4 + 4r + r2 = 32 + 4

Combine like terms: 32 + 4 = 36
4 + 4r + r2 = 36

Factor a perfect square on the left side:
(r + 2)(r + 2) = 36

Calculate the square root of the right side: 6

Break this problem into two subproblems by setting 
(r + 2) equal to 6 and -6.

Subproblem 1

r + 2 = 6 Simplifying r + 2 = 6 Reorder the terms: 2 + r = 6 Solving 2 + r = 6 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 = 6 + -2 Combine like terms: 2 + -2 = 0 0 + r = 6 + -2 r = 6 + -2 Combine like terms: 6 + -2 = 4 r = 4 Simplifying r = 4

Subproblem 2

r + 2 = -6 Simplifying r + 2 = -6 Reorder the terms: 2 + r = -6 Solving 2 + r = -6 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 = -6 + -2 Combine like terms: 2 + -2 = 0 0 + r = -6 + -2 r = -6 + -2 Combine like terms: -6 + -2 = -8 r = -8 Simplifying r = -8

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4, -8}

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