-5r^2+8r+2=0

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Solution for -5r^2+8r+2=0 equation:


Simplifying
-5r2 + 8r + 2 = 0

Reorder the terms:
2 + 8r + -5r2 = 0

Solving
2 + 8r + -5r2 = 0

Solving for variable 'r'.

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

Divide each side by '-5'.
-0.4 + -1.6r + r2 = 0

Move the constant term to the right:

Add '0.4' to each side of the equation.
-0.4 + -1.6r + 0.4 + r2 = 0 + 0.4

Reorder the terms:
-0.4 + 0.4 + -1.6r + r2 = 0 + 0.4

Combine like terms: -0.4 + 0.4 = 0.0
0.0 + -1.6r + r2 = 0 + 0.4
-1.6r + r2 = 0 + 0.4

Combine like terms: 0 + 0.4 = 0.4
-1.6r + r2 = 0.4

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 = 0.4 + 0.64

Reorder the terms:
0.64 + -1.6r + r2 = 0.4 + 0.64

Combine like terms: 0.4 + 0.64 = 1.04
0.64 + -1.6r + r2 = 1.04

Factor a perfect square on the left side:
(r + -0.8)(r + -0.8) = 1.04

Calculate the square root of the right side: 1.019803903

Break this problem into two subproblems by setting 
(r + -0.8) equal to 1.019803903 and -1.019803903.

Subproblem 1

r + -0.8 = 1.019803903 Simplifying r + -0.8 = 1.019803903 Reorder the terms: -0.8 + r = 1.019803903 Solving -0.8 + r = 1.019803903 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 = 1.019803903 + 0.8 Combine like terms: -0.8 + 0.8 = 0.0 0.0 + r = 1.019803903 + 0.8 r = 1.019803903 + 0.8 Combine like terms: 1.019803903 + 0.8 = 1.819803903 r = 1.819803903 Simplifying r = 1.819803903

Subproblem 2

r + -0.8 = -1.019803903 Simplifying r + -0.8 = -1.019803903 Reorder the terms: -0.8 + r = -1.019803903 Solving -0.8 + r = -1.019803903 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 = -1.019803903 + 0.8 Combine like terms: -0.8 + 0.8 = 0.0 0.0 + r = -1.019803903 + 0.8 r = -1.019803903 + 0.8 Combine like terms: -1.019803903 + 0.8 = -0.219803903 r = -0.219803903 Simplifying r = -0.219803903

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.819803903, -0.219803903}

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