756.74=2*3.14*r^2+2*3.14*r*19.1

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Solution for 756.74=2*3.14*r^2+2*3.14*r*19.1 equation:


Simplifying
756.74 = 2 * 3.14r2 + 2 * 3.14r * 19.1

Multiply 2 * 3.14
756.74 = 6.28r2 + 2 * 3.14r * 19.1

Reorder the terms for easier multiplication:
756.74 = 6.28r2 + 2 * 3.14 * 19.1r

Multiply 2 * 3.14
756.74 = 6.28r2 + 6.28 * 19.1r

Multiply 6.28 * 19.1
756.74 = 6.28r2 + 119.948r

Reorder the terms:
756.74 = 119.948r + 6.28r2

Solving
756.74 = 119.948r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
756.74 + -119.948r + -6.28r2 = 119.948r + -119.948r + 6.28r2 + -6.28r2

Combine like terms: 119.948r + -119.948r = 0.000
756.74 + -119.948r + -6.28r2 = 0.000 + 6.28r2 + -6.28r2
756.74 + -119.948r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
756.74 + -119.948r + -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'.
-120.5 + 19.1r + r2 = 0

Move the constant term to the right:

Add '120.5' to each side of the equation.
-120.5 + 19.1r + 120.5 + r2 = 0 + 120.5

Reorder the terms:
-120.5 + 120.5 + 19.1r + r2 = 0 + 120.5

Combine like terms: -120.5 + 120.5 = 0.0
0.0 + 19.1r + r2 = 0 + 120.5
19.1r + r2 = 0 + 120.5

Combine like terms: 0 + 120.5 = 120.5
19.1r + r2 = 120.5

The r term is 19.1r.  Take half its coefficient (9.55).
Square it (91.2025) and add it to both sides.

Add '91.2025' to each side of the equation.
19.1r + 91.2025 + r2 = 120.5 + 91.2025

Reorder the terms:
91.2025 + 19.1r + r2 = 120.5 + 91.2025

Combine like terms: 120.5 + 91.2025 = 211.7025
91.2025 + 19.1r + r2 = 211.7025

Factor a perfect square on the left side:
(r + 9.55)(r + 9.55) = 211.7025

Calculate the square root of the right side: 14.55

Break this problem into two subproblems by setting 
(r + 9.55) equal to 14.55 and -14.55.

Subproblem 1

r + 9.55 = 14.55 Simplifying r + 9.55 = 14.55 Reorder the terms: 9.55 + r = 14.55 Solving 9.55 + r = 14.55 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-9.55' to each side of the equation. 9.55 + -9.55 + r = 14.55 + -9.55 Combine like terms: 9.55 + -9.55 = 0.00 0.00 + r = 14.55 + -9.55 r = 14.55 + -9.55 Combine like terms: 14.55 + -9.55 = 5 r = 5 Simplifying r = 5

Subproblem 2

r + 9.55 = -14.55 Simplifying r + 9.55 = -14.55 Reorder the terms: 9.55 + r = -14.55 Solving 9.55 + r = -14.55 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-9.55' to each side of the equation. 9.55 + -9.55 + r = -14.55 + -9.55 Combine like terms: 9.55 + -9.55 = 0.00 0.00 + r = -14.55 + -9.55 r = -14.55 + -9.55 Combine like terms: -14.55 + -9.55 = -24.1 r = -24.1 Simplifying r = -24.1

Solution

The solution to the problem is based on the solutions from the subproblems. r = {5, -24.1}

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