5r^2-8r=3

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Solution for 5r^2-8r=3 equation:


Simplifying
5r2 + -8r = 3

Reorder the terms:
-8r + 5r2 = 3

Solving
-8r + 5r2 = 3

Solving for variable 'r'.

Reorder the terms:
-3 + -8r + 5r2 = 3 + -3

Combine like terms: 3 + -3 = 0
-3 + -8r + 5r2 = 0

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

Divide each side by '5'.
-0.6 + -1.6r + r2 = 0

Move the constant term to the right:

Add '0.6' to each side of the equation.
-0.6 + -1.6r + 0.6 + r2 = 0 + 0.6

Reorder the terms:
-0.6 + 0.6 + -1.6r + r2 = 0 + 0.6

Combine like terms: -0.6 + 0.6 = 0.0
0.0 + -1.6r + r2 = 0 + 0.6
-1.6r + r2 = 0 + 0.6

Combine like terms: 0 + 0.6 = 0.6
-1.6r + r2 = 0.6

The r term is -1.6r.  Take half its coefficient (-0.8).
Square it (0.64) and add it to both sides.

Add '0.64' to each side of the equation.
-1.6r + 0.64 + r2 = 0.6 + 0.64

Reorder the terms:
0.64 + -1.6r + r2 = 0.6 + 0.64

Combine like terms: 0.6 + 0.64 = 1.24
0.64 + -1.6r + r2 = 1.24

Factor a perfect square on the left side:
(r + -0.8)(r + -0.8) = 1.24

Calculate the square root of the right side: 1.113552873

Break this problem into two subproblems by setting 
(r + -0.8) equal to 1.113552873 and -1.113552873.

Subproblem 1

r + -0.8 = 1.113552873 Simplifying r + -0.8 = 1.113552873 Reorder the terms: -0.8 + r = 1.113552873 Solving -0.8 + r = 1.113552873 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.8' to each side of the equation. -0.8 + 0.8 + r = 1.113552873 + 0.8 Combine like terms: -0.8 + 0.8 = 0.0 0.0 + r = 1.113552873 + 0.8 r = 1.113552873 + 0.8 Combine like terms: 1.113552873 + 0.8 = 1.913552873 r = 1.913552873 Simplifying r = 1.913552873

Subproblem 2

r + -0.8 = -1.113552873 Simplifying r + -0.8 = -1.113552873 Reorder the terms: -0.8 + r = -1.113552873 Solving -0.8 + r = -1.113552873 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.8' to each side of the equation. -0.8 + 0.8 + r = -1.113552873 + 0.8 Combine like terms: -0.8 + 0.8 = 0.0 0.0 + r = -1.113552873 + 0.8 r = -1.113552873 + 0.8 Combine like terms: -1.113552873 + 0.8 = -0.313552873 r = -0.313552873 Simplifying r = -0.313552873

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.913552873, -0.313552873}

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