2458.2432=2*3.14*r^2+2*3.14*r*4.2

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Solution for 2458.2432=2*3.14*r^2+2*3.14*r*4.2 equation:


Simplifying
2458.2432 = 2 * 3.14r2 + 2 * 3.14r * 4.2

Multiply 2 * 3.14
2458.2432 = 6.28r2 + 2 * 3.14r * 4.2

Reorder the terms for easier multiplication:
2458.2432 = 6.28r2 + 2 * 3.14 * 4.2r

Multiply 2 * 3.14
2458.2432 = 6.28r2 + 6.28 * 4.2r

Multiply 6.28 * 4.2
2458.2432 = 6.28r2 + 26.376r

Reorder the terms:
2458.2432 = 26.376r + 6.28r2

Solving
2458.2432 = 26.376r + 6.28r2

Solving for variable 'r'.

Reorder the terms:
2458.2432 + -26.376r + -6.28r2 = 26.376r + -26.376r + 6.28r2 + -6.28r2

Combine like terms: 26.376r + -26.376r = 0.000
2458.2432 + -26.376r + -6.28r2 = 0.000 + 6.28r2 + -6.28r2
2458.2432 + -26.376r + -6.28r2 = 6.28r2 + -6.28r2

Combine like terms: 6.28r2 + -6.28r2 = 0.00
2458.2432 + -26.376r + -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'.
-391.44 + 4.2r + r2 = 0

Move the constant term to the right:

Add '391.44' to each side of the equation.
-391.44 + 4.2r + 391.44 + r2 = 0 + 391.44

Reorder the terms:
-391.44 + 391.44 + 4.2r + r2 = 0 + 391.44

Combine like terms: -391.44 + 391.44 = 0.00
0.00 + 4.2r + r2 = 0 + 391.44
4.2r + r2 = 0 + 391.44

Combine like terms: 0 + 391.44 = 391.44
4.2r + r2 = 391.44

The r term is 4.2r.  Take half its coefficient (2.1).
Square it (4.41) and add it to both sides.

Add '4.41' to each side of the equation.
4.2r + 4.41 + r2 = 391.44 + 4.41

Reorder the terms:
4.41 + 4.2r + r2 = 391.44 + 4.41

Combine like terms: 391.44 + 4.41 = 395.85
4.41 + 4.2r + r2 = 395.85

Factor a perfect square on the left side:
(r + 2.1)(r + 2.1) = 395.85

Calculate the square root of the right side: 19.895979493

Break this problem into two subproblems by setting 
(r + 2.1) equal to 19.895979493 and -19.895979493.

Subproblem 1

r + 2.1 = 19.895979493 Simplifying r + 2.1 = 19.895979493 Reorder the terms: 2.1 + r = 19.895979493 Solving 2.1 + r = 19.895979493 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2.1' to each side of the equation. 2.1 + -2.1 + r = 19.895979493 + -2.1 Combine like terms: 2.1 + -2.1 = 0.0 0.0 + r = 19.895979493 + -2.1 r = 19.895979493 + -2.1 Combine like terms: 19.895979493 + -2.1 = 17.795979493 r = 17.795979493 Simplifying r = 17.795979493

Subproblem 2

r + 2.1 = -19.895979493 Simplifying r + 2.1 = -19.895979493 Reorder the terms: 2.1 + r = -19.895979493 Solving 2.1 + r = -19.895979493 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2.1' to each side of the equation. 2.1 + -2.1 + r = -19.895979493 + -2.1 Combine like terms: 2.1 + -2.1 = 0.0 0.0 + r = -19.895979493 + -2.1 r = -19.895979493 + -2.1 Combine like terms: -19.895979493 + -2.1 = -21.995979493 r = -21.995979493 Simplifying r = -21.995979493

Solution

The solution to the problem is based on the solutions from the subproblems. r = {17.795979493, -21.995979493}

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