-8r^2+64r+19=0

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Solution for -8r^2+64r+19=0 equation:


Simplifying
-8r2 + 64r + 19 = 0

Reorder the terms:
19 + 64r + -8r2 = 0

Solving
19 + 64r + -8r2 = 0

Solving for variable 'r'.

Begin completing the square.  Divide all terms by
-8 the coefficient of the squared term: 

Divide each side by '-8'.
-2.375 + -8r + r2 = 0

Move the constant term to the right:

Add '2.375' to each side of the equation.
-2.375 + -8r + 2.375 + r2 = 0 + 2.375

Reorder the terms:
-2.375 + 2.375 + -8r + r2 = 0 + 2.375

Combine like terms: -2.375 + 2.375 = 0.000
0.000 + -8r + r2 = 0 + 2.375
-8r + r2 = 0 + 2.375

Combine like terms: 0 + 2.375 = 2.375
-8r + r2 = 2.375

The r term is -8r.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8r + 16 + r2 = 2.375 + 16

Reorder the terms:
16 + -8r + r2 = 2.375 + 16

Combine like terms: 2.375 + 16 = 18.375
16 + -8r + r2 = 18.375

Factor a perfect square on the left side:
(r + -4)(r + -4) = 18.375

Calculate the square root of the right side: 4.28660705

Break this problem into two subproblems by setting 
(r + -4) equal to 4.28660705 and -4.28660705.

Subproblem 1

r + -4 = 4.28660705 Simplifying r + -4 = 4.28660705 Reorder the terms: -4 + r = 4.28660705 Solving -4 + r = 4.28660705 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + r = 4.28660705 + 4 Combine like terms: -4 + 4 = 0 0 + r = 4.28660705 + 4 r = 4.28660705 + 4 Combine like terms: 4.28660705 + 4 = 8.28660705 r = 8.28660705 Simplifying r = 8.28660705

Subproblem 2

r + -4 = -4.28660705 Simplifying r + -4 = -4.28660705 Reorder the terms: -4 + r = -4.28660705 Solving -4 + r = -4.28660705 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + r = -4.28660705 + 4 Combine like terms: -4 + 4 = 0 0 + r = -4.28660705 + 4 r = -4.28660705 + 4 Combine like terms: -4.28660705 + 4 = -0.28660705 r = -0.28660705 Simplifying r = -0.28660705

Solution

The solution to the problem is based on the solutions from the subproblems. r = {8.28660705, -0.28660705}

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