2*3.14r^2+2*3.14r(7.7)=193.0472

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Solution for 2*3.14r^2+2*3.14r(7.7)=193.0472 equation:


Simplifying
2 * 3.14r2 + 2 * 3.14r(7.7) = 193.0472

Multiply 2 * 3.14
6.28r2 + 2 * 3.14r(7.7) = 193.0472

Reorder the terms for easier multiplication:
6.28r2 + 2 * 3.14 * 7.7r = 193.0472

Multiply 2 * 3.14
6.28r2 + 6.28 * 7.7r = 193.0472

Multiply 6.28 * 7.7
6.28r2 + 48.356r = 193.0472

Reorder the terms:
48.356r + 6.28r2 = 193.0472

Solving
48.356r + 6.28r2 = 193.0472

Solving for variable 'r'.

Reorder the terms:
-193.0472 + 48.356r + 6.28r2 = 193.0472 + -193.0472

Combine like terms: 193.0472 + -193.0472 = 0.0000
-193.0472 + 48.356r + 6.28r2 = 0.0000

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

Divide each side by '6.28'.
-30.74 + 7.7r + r2 = 0.00

Move the constant term to the right:

Add '30.74' to each side of the equation.
-30.74 + 7.7r + 30.74 + r2 = 0.00 + 30.74

Reorder the terms:
-30.74 + 30.74 + 7.7r + r2 = 0.00 + 30.74

Combine like terms: -30.74 + 30.74 = 0.00
0.00 + 7.7r + r2 = 0.00 + 30.74
7.7r + r2 = 0.00 + 30.74

Combine like terms: 0.00 + 30.74 = 30.74
7.7r + r2 = 30.74

The r term is 7.7r.  Take half its coefficient (3.85).
Square it (14.8225) and add it to both sides.

Add '14.8225' to each side of the equation.
7.7r + 14.8225 + r2 = 30.74 + 14.8225

Reorder the terms:
14.8225 + 7.7r + r2 = 30.74 + 14.8225

Combine like terms: 30.74 + 14.8225 = 45.5625
14.8225 + 7.7r + r2 = 45.5625

Factor a perfect square on the left side:
(r + 3.85)(r + 3.85) = 45.5625

Calculate the square root of the right side: 6.75

Break this problem into two subproblems by setting 
(r + 3.85) equal to 6.75 and -6.75.

Subproblem 1

r + 3.85 = 6.75 Simplifying r + 3.85 = 6.75 Reorder the terms: 3.85 + r = 6.75 Solving 3.85 + r = 6.75 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-3.85' to each side of the equation. 3.85 + -3.85 + r = 6.75 + -3.85 Combine like terms: 3.85 + -3.85 = 0.00 0.00 + r = 6.75 + -3.85 r = 6.75 + -3.85 Combine like terms: 6.75 + -3.85 = 2.9 r = 2.9 Simplifying r = 2.9

Subproblem 2

r + 3.85 = -6.75 Simplifying r + 3.85 = -6.75 Reorder the terms: 3.85 + r = -6.75 Solving 3.85 + r = -6.75 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-3.85' to each side of the equation. 3.85 + -3.85 + r = -6.75 + -3.85 Combine like terms: 3.85 + -3.85 = 0.00 0.00 + r = -6.75 + -3.85 r = -6.75 + -3.85 Combine like terms: -6.75 + -3.85 = -10.6 r = -10.6 Simplifying r = -10.6

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.9, -10.6}

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