7r^2+8r-4=0

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Solution for 7r^2+8r-4=0 equation:


Simplifying
7r2 + 8r + -4 = 0

Reorder the terms:
-4 + 8r + 7r2 = 0

Solving
-4 + 8r + 7r2 = 0

Solving for variable 'r'.

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

Divide each side by '7'.
-0.5714285714 + 1.142857143r + r2 = 0

Move the constant term to the right:

Add '0.5714285714' to each side of the equation.
-0.5714285714 + 1.142857143r + 0.5714285714 + r2 = 0 + 0.5714285714

Reorder the terms:
-0.5714285714 + 0.5714285714 + 1.142857143r + r2 = 0 + 0.5714285714

Combine like terms: -0.5714285714 + 0.5714285714 = 0.0000000000
0.0000000000 + 1.142857143r + r2 = 0 + 0.5714285714
1.142857143r + r2 = 0 + 0.5714285714

Combine like terms: 0 + 0.5714285714 = 0.5714285714
1.142857143r + r2 = 0.5714285714

The r term is 1.142857143r.  Take half its coefficient (0.5714285715).
Square it (0.3265306123) and add it to both sides.

Add '0.3265306123' to each side of the equation.
1.142857143r + 0.3265306123 + r2 = 0.5714285714 + 0.3265306123

Reorder the terms:
0.3265306123 + 1.142857143r + r2 = 0.5714285714 + 0.3265306123

Combine like terms: 0.5714285714 + 0.3265306123 = 0.8979591837
0.3265306123 + 1.142857143r + r2 = 0.8979591837

Factor a perfect square on the left side:
(r + 0.5714285715)(r + 0.5714285715) = 0.8979591837

Calculate the square root of the right side: 0.947607083

Break this problem into two subproblems by setting 
(r + 0.5714285715) equal to 0.947607083 and -0.947607083.

Subproblem 1

r + 0.5714285715 = 0.947607083 Simplifying r + 0.5714285715 = 0.947607083 Reorder the terms: 0.5714285715 + r = 0.947607083 Solving 0.5714285715 + r = 0.947607083 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-0.5714285715' to each side of the equation. 0.5714285715 + -0.5714285715 + r = 0.947607083 + -0.5714285715 Combine like terms: 0.5714285715 + -0.5714285715 = 0.0000000000 0.0000000000 + r = 0.947607083 + -0.5714285715 r = 0.947607083 + -0.5714285715 Combine like terms: 0.947607083 + -0.5714285715 = 0.3761785115 r = 0.3761785115 Simplifying r = 0.3761785115

Subproblem 2

r + 0.5714285715 = -0.947607083 Simplifying r + 0.5714285715 = -0.947607083 Reorder the terms: 0.5714285715 + r = -0.947607083 Solving 0.5714285715 + r = -0.947607083 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-0.5714285715' to each side of the equation. 0.5714285715 + -0.5714285715 + r = -0.947607083 + -0.5714285715 Combine like terms: 0.5714285715 + -0.5714285715 = 0.0000000000 0.0000000000 + r = -0.947607083 + -0.5714285715 r = -0.947607083 + -0.5714285715 Combine like terms: -0.947607083 + -0.5714285715 = -1.5190356545 r = -1.5190356545 Simplifying r = -1.5190356545

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.3761785115, -1.5190356545}

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