742.61=2*3.14*r(r)+2*3.14*r*16

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Solution for 742.61=2*3.14*r(r)+2*3.14*r*16 equation:


Simplifying
742.61 = 2 * 3.14r(r) + 2 * 3.14r * 16

Multiply 2 * 3.14
742.61 = 6.28r * r + 2 * 3.14r * 16

Multiply r * r
742.61 = 6.28r2 + 2 * 3.14r * 16

Reorder the terms for easier multiplication:
742.61 = 6.28r2 + 2 * 3.14 * 16r

Multiply 2 * 3.14
742.61 = 6.28r2 + 6.28 * 16r

Multiply 6.28 * 16
742.61 = 6.28r2 + 100.48r

Reorder the terms:
742.61 = 100.48r + 6.28r2

Solving
742.61 = 100.48r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
742.61 + -100.48r + -6.28r2 = 100.48r + -100.48r + 6.28r2 + -6.28r2

Combine like terms: 100.48r + -100.48r = 0.00
742.61 + -100.48r + -6.28r2 = 0.00 + 6.28r2 + -6.28r2
742.61 + -100.48r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
742.61 + -100.48r + -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'.
-118.25 + 16r + r2 = 0

Move the constant term to the right:

Add '118.25' to each side of the equation.
-118.25 + 16r + 118.25 + r2 = 0 + 118.25

Reorder the terms:
-118.25 + 118.25 + 16r + r2 = 0 + 118.25

Combine like terms: -118.25 + 118.25 = 0.00
0.00 + 16r + r2 = 0 + 118.25
16r + r2 = 0 + 118.25

Combine like terms: 0 + 118.25 = 118.25
16r + r2 = 118.25

The r term is 16r.  Take half its coefficient (8).
Square it (64) and add it to both sides.

Add '64' to each side of the equation.
16r + 64 + r2 = 118.25 + 64

Reorder the terms:
64 + 16r + r2 = 118.25 + 64

Combine like terms: 118.25 + 64 = 182.25
64 + 16r + r2 = 182.25

Factor a perfect square on the left side:
(r + 8)(r + 8) = 182.25

Calculate the square root of the right side: 13.5

Break this problem into two subproblems by setting 
(r + 8) equal to 13.5 and -13.5.

Subproblem 1

r + 8 = 13.5 Simplifying r + 8 = 13.5 Reorder the terms: 8 + r = 13.5 Solving 8 + r = 13.5 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-8' to each side of the equation. 8 + -8 + r = 13.5 + -8 Combine like terms: 8 + -8 = 0 0 + r = 13.5 + -8 r = 13.5 + -8 Combine like terms: 13.5 + -8 = 5.5 r = 5.5 Simplifying r = 5.5

Subproblem 2

r + 8 = -13.5 Simplifying r + 8 = -13.5 Reorder the terms: 8 + r = -13.5 Solving 8 + r = -13.5 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-8' to each side of the equation. 8 + -8 + r = -13.5 + -8 Combine like terms: 8 + -8 = 0 0 + r = -13.5 + -8 r = -13.5 + -8 Combine like terms: -13.5 + -8 = -21.5 r = -21.5 Simplifying r = -21.5

Solution

The solution to the problem is based on the solutions from the subproblems. r = {5.5, -21.5}

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