-5r^2+5r+4=0

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Solution for -5r^2+5r+4=0 equation:


Simplifying
-5r2 + 5r + 4 = 0

Reorder the terms:
4 + 5r + -5r2 = 0

Solving
4 + 5r + -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'.
-0.8 + -1r + r2 = 0

Move the constant term to the right:

Add '0.8' to each side of the equation.
-0.8 + -1r + 0.8 + r2 = 0 + 0.8

Reorder the terms:
-0.8 + 0.8 + -1r + r2 = 0 + 0.8

Combine like terms: -0.8 + 0.8 = 0.0
0.0 + -1r + r2 = 0 + 0.8
-1r + r2 = 0 + 0.8

Combine like terms: 0 + 0.8 = 0.8
-1r + r2 = 0.8

The r term is -1r.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1r + 0.25 + r2 = 0.8 + 0.25

Reorder the terms:
0.25 + -1r + r2 = 0.8 + 0.25

Combine like terms: 0.8 + 0.25 = 1.05
0.25 + -1r + r2 = 1.05

Factor a perfect square on the left side:
(r + -0.5)(r + -0.5) = 1.05

Calculate the square root of the right side: 1.024695077

Break this problem into two subproblems by setting 
(r + -0.5) equal to 1.024695077 and -1.024695077.

Subproblem 1

r + -0.5 = 1.024695077 Simplifying r + -0.5 = 1.024695077 Reorder the terms: -0.5 + r = 1.024695077 Solving -0.5 + r = 1.024695077 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = 1.024695077 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = 1.024695077 + 0.5 r = 1.024695077 + 0.5 Combine like terms: 1.024695077 + 0.5 = 1.524695077 r = 1.524695077 Simplifying r = 1.524695077

Subproblem 2

r + -0.5 = -1.024695077 Simplifying r + -0.5 = -1.024695077 Reorder the terms: -0.5 + r = -1.024695077 Solving -0.5 + r = -1.024695077 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = -1.024695077 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = -1.024695077 + 0.5 r = -1.024695077 + 0.5 Combine like terms: -1.024695077 + 0.5 = -0.524695077 r = -0.524695077 Simplifying r = -0.524695077

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.524695077, -0.524695077}

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