7r^2-8r-9=0

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Solution for 7r^2-8r-9=0 equation:


Simplifying
7r2 + -8r + -9 = 0

Reorder the terms:
-9 + -8r + 7r2 = 0

Solving
-9 + -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'.
-1.285714286 + -1.142857143r + r2 = 0

Move the constant term to the right:

Add '1.285714286' to each side of the equation.
-1.285714286 + -1.142857143r + 1.285714286 + r2 = 0 + 1.285714286

Reorder the terms:
-1.285714286 + 1.285714286 + -1.142857143r + r2 = 0 + 1.285714286

Combine like terms: -1.285714286 + 1.285714286 = 0.000000000
0.000000000 + -1.142857143r + r2 = 0 + 1.285714286
-1.142857143r + r2 = 0 + 1.285714286

Combine like terms: 0 + 1.285714286 = 1.285714286
-1.142857143r + r2 = 1.285714286

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 = 1.285714286 + 0.3265306123

Reorder the terms:
0.3265306123 + -1.142857143r + r2 = 1.285714286 + 0.3265306123

Combine like terms: 1.285714286 + 0.3265306123 = 1.6122448983
0.3265306123 + -1.142857143r + r2 = 1.6122448983

Factor a perfect square on the left side:
(r + -0.5714285715)(r + -0.5714285715) = 1.6122448983

Calculate the square root of the right side: 1.26974206

Break this problem into two subproblems by setting 
(r + -0.5714285715) equal to 1.26974206 and -1.26974206.

Subproblem 1

r + -0.5714285715 = 1.26974206 Simplifying r + -0.5714285715 = 1.26974206 Reorder the terms: -0.5714285715 + r = 1.26974206 Solving -0.5714285715 + r = 1.26974206 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 = 1.26974206 + 0.5714285715 Combine like terms: -0.5714285715 + 0.5714285715 = 0.0000000000 0.0000000000 + r = 1.26974206 + 0.5714285715 r = 1.26974206 + 0.5714285715 Combine like terms: 1.26974206 + 0.5714285715 = 1.8411706315 r = 1.8411706315 Simplifying r = 1.8411706315

Subproblem 2

r + -0.5714285715 = -1.26974206 Simplifying r + -0.5714285715 = -1.26974206 Reorder the terms: -0.5714285715 + r = -1.26974206 Solving -0.5714285715 + r = -1.26974206 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 = -1.26974206 + 0.5714285715 Combine like terms: -0.5714285715 + 0.5714285715 = 0.0000000000 0.0000000000 + r = -1.26974206 + 0.5714285715 r = -1.26974206 + 0.5714285715 Combine like terms: -1.26974206 + 0.5714285715 = -0.6983134885 r = -0.6983134885 Simplifying r = -0.6983134885

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.8411706315, -0.6983134885}

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