5(r-4)r=9

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Solution for 5(r-4)r=9 equation:


Simplifying
5(r + -4) * r = 9

Reorder the terms:
5(-4 + r) * r = 9

Reorder the terms for easier multiplication:
5r(-4 + r) = 9
(-4 * 5r + r * 5r) = 9
(-20r + 5r2) = 9

Solving
-20r + 5r2 = 9

Solving for variable 'r'.

Reorder the terms:
-9 + -20r + 5r2 = 9 + -9

Combine like terms: 9 + -9 = 0
-9 + -20r + 5r2 = 0

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

Divide each side by '5'.
-1.8 + -4r + r2 = 0

Move the constant term to the right:

Add '1.8' to each side of the equation.
-1.8 + -4r + 1.8 + r2 = 0 + 1.8

Reorder the terms:
-1.8 + 1.8 + -4r + r2 = 0 + 1.8

Combine like terms: -1.8 + 1.8 = 0.0
0.0 + -4r + r2 = 0 + 1.8
-4r + r2 = 0 + 1.8

Combine like terms: 0 + 1.8 = 1.8
-4r + r2 = 1.8

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 = 1.8 + 4

Reorder the terms:
4 + -4r + r2 = 1.8 + 4

Combine like terms: 1.8 + 4 = 5.8
4 + -4r + r2 = 5.8

Factor a perfect square on the left side:
(r + -2)(r + -2) = 5.8

Calculate the square root of the right side: 2.408318916

Break this problem into two subproblems by setting 
(r + -2) equal to 2.408318916 and -2.408318916.

Subproblem 1

r + -2 = 2.408318916 Simplifying r + -2 = 2.408318916 Reorder the terms: -2 + r = 2.408318916 Solving -2 + r = 2.408318916 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 = 2.408318916 + 2 Combine like terms: -2 + 2 = 0 0 + r = 2.408318916 + 2 r = 2.408318916 + 2 Combine like terms: 2.408318916 + 2 = 4.408318916 r = 4.408318916 Simplifying r = 4.408318916

Subproblem 2

r + -2 = -2.408318916 Simplifying r + -2 = -2.408318916 Reorder the terms: -2 + r = -2.408318916 Solving -2 + r = -2.408318916 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 = -2.408318916 + 2 Combine like terms: -2 + 2 = 0 0 + r = -2.408318916 + 2 r = -2.408318916 + 2 Combine like terms: -2.408318916 + 2 = -0.408318916 r = -0.408318916 Simplifying r = -0.408318916

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4.408318916, -0.408318916}

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