2r^2+4r-5=0

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


Simplifying
2r2 + 4r + -5 = 0

Reorder the terms:
-5 + 4r + 2r2 = 0

Solving
-5 + 4r + 2r2 = 0

Solving for variable 'r'.

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

Divide each side by '2'.
-2.5 + 2r + r2 = 0

Move the constant term to the right:

Add '2.5' to each side of the equation.
-2.5 + 2r + 2.5 + r2 = 0 + 2.5

Reorder the terms:
-2.5 + 2.5 + 2r + r2 = 0 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + 2r + r2 = 0 + 2.5
2r + r2 = 0 + 2.5

Combine like terms: 0 + 2.5 = 2.5
2r + r2 = 2.5

The r term is 2r.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2r + 1 + r2 = 2.5 + 1

Reorder the terms:
1 + 2r + r2 = 2.5 + 1

Combine like terms: 2.5 + 1 = 3.5
1 + 2r + r2 = 3.5

Factor a perfect square on the left side:
(r + 1)(r + 1) = 3.5

Calculate the square root of the right side: 1.870828693

Break this problem into two subproblems by setting 
(r + 1) equal to 1.870828693 and -1.870828693.

Subproblem 1

r + 1 = 1.870828693 Simplifying r + 1 = 1.870828693 Reorder the terms: 1 + r = 1.870828693 Solving 1 + r = 1.870828693 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + r = 1.870828693 + -1 Combine like terms: 1 + -1 = 0 0 + r = 1.870828693 + -1 r = 1.870828693 + -1 Combine like terms: 1.870828693 + -1 = 0.870828693 r = 0.870828693 Simplifying r = 0.870828693

Subproblem 2

r + 1 = -1.870828693 Simplifying r + 1 = -1.870828693 Reorder the terms: 1 + r = -1.870828693 Solving 1 + r = -1.870828693 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + r = -1.870828693 + -1 Combine like terms: 1 + -1 = 0 0 + r = -1.870828693 + -1 r = -1.870828693 + -1 Combine like terms: -1.870828693 + -1 = -2.870828693 r = -2.870828693 Simplifying r = -2.870828693

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.870828693, -2.870828693}

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