7r^2-2r-8=0

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


Simplifying
7r2 + -2r + -8 = 0

Reorder the terms:
-8 + -2r + 7r2 = 0

Solving
-8 + -2r + 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'.
-1.142857143 + -0.2857142857r + r2 = 0

Move the constant term to the right:

Add '1.142857143' to each side of the equation.
-1.142857143 + -0.2857142857r + 1.142857143 + r2 = 0 + 1.142857143

Reorder the terms:
-1.142857143 + 1.142857143 + -0.2857142857r + r2 = 0 + 1.142857143

Combine like terms: -1.142857143 + 1.142857143 = 0.000000000
0.000000000 + -0.2857142857r + r2 = 0 + 1.142857143
-0.2857142857r + r2 = 0 + 1.142857143

Combine like terms: 0 + 1.142857143 = 1.142857143
-0.2857142857r + r2 = 1.142857143

The r term is -0.2857142857r.  Take half its coefficient (-0.1428571429).
Square it (0.02040816328) and add it to both sides.

Add '0.02040816328' to each side of the equation.
-0.2857142857r + 0.02040816328 + r2 = 1.142857143 + 0.02040816328

Reorder the terms:
0.02040816328 + -0.2857142857r + r2 = 1.142857143 + 0.02040816328

Combine like terms: 1.142857143 + 0.02040816328 = 1.16326530628
0.02040816328 + -0.2857142857r + r2 = 1.16326530628

Factor a perfect square on the left side:
(r + -0.1428571429)(r + -0.1428571429) = 1.16326530628

Calculate the square root of the right side: 1.078547777

Break this problem into two subproblems by setting 
(r + -0.1428571429) equal to 1.078547777 and -1.078547777.

Subproblem 1

r + -0.1428571429 = 1.078547777 Simplifying r + -0.1428571429 = 1.078547777 Reorder the terms: -0.1428571429 + r = 1.078547777 Solving -0.1428571429 + r = 1.078547777 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.1428571429' to each side of the equation. -0.1428571429 + 0.1428571429 + r = 1.078547777 + 0.1428571429 Combine like terms: -0.1428571429 + 0.1428571429 = 0.0000000000 0.0000000000 + r = 1.078547777 + 0.1428571429 r = 1.078547777 + 0.1428571429 Combine like terms: 1.078547777 + 0.1428571429 = 1.2214049199 r = 1.2214049199 Simplifying r = 1.2214049199

Subproblem 2

r + -0.1428571429 = -1.078547777 Simplifying r + -0.1428571429 = -1.078547777 Reorder the terms: -0.1428571429 + r = -1.078547777 Solving -0.1428571429 + r = -1.078547777 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.1428571429' to each side of the equation. -0.1428571429 + 0.1428571429 + r = -1.078547777 + 0.1428571429 Combine like terms: -0.1428571429 + 0.1428571429 = 0.0000000000 0.0000000000 + r = -1.078547777 + 0.1428571429 r = -1.078547777 + 0.1428571429 Combine like terms: -1.078547777 + 0.1428571429 = -0.9356906341 r = -0.9356906341 Simplifying r = -0.9356906341

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.2214049199, -0.9356906341}

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