5r^2-54r-80=0

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Solution for 5r^2-54r-80=0 equation:


Simplifying
5r2 + -54r + -80 = 0

Reorder the terms:
-80 + -54r + 5r2 = 0

Solving
-80 + -54r + 5r2 = 0

Solving for variable 'r'.

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

Divide each side by '5'.
-16 + -10.8r + r2 = 0

Move the constant term to the right:

Add '16' to each side of the equation.
-16 + -10.8r + 16 + r2 = 0 + 16

Reorder the terms:
-16 + 16 + -10.8r + r2 = 0 + 16

Combine like terms: -16 + 16 = 0
0 + -10.8r + r2 = 0 + 16
-10.8r + r2 = 0 + 16

Combine like terms: 0 + 16 = 16
-10.8r + r2 = 16

The r term is -10.8r.  Take half its coefficient (-5.4).
Square it (29.16) and add it to both sides.

Add '29.16' to each side of the equation.
-10.8r + 29.16 + r2 = 16 + 29.16

Reorder the terms:
29.16 + -10.8r + r2 = 16 + 29.16

Combine like terms: 16 + 29.16 = 45.16
29.16 + -10.8r + r2 = 45.16

Factor a perfect square on the left side:
(r + -5.4)(r + -5.4) = 45.16

Calculate the square root of the right side: 6.720119047

Break this problem into two subproblems by setting 
(r + -5.4) equal to 6.720119047 and -6.720119047.

Subproblem 1

r + -5.4 = 6.720119047 Simplifying r + -5.4 = 6.720119047 Reorder the terms: -5.4 + r = 6.720119047 Solving -5.4 + r = 6.720119047 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '5.4' to each side of the equation. -5.4 + 5.4 + r = 6.720119047 + 5.4 Combine like terms: -5.4 + 5.4 = 0.0 0.0 + r = 6.720119047 + 5.4 r = 6.720119047 + 5.4 Combine like terms: 6.720119047 + 5.4 = 12.120119047 r = 12.120119047 Simplifying r = 12.120119047

Subproblem 2

r + -5.4 = -6.720119047 Simplifying r + -5.4 = -6.720119047 Reorder the terms: -5.4 + r = -6.720119047 Solving -5.4 + r = -6.720119047 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '5.4' to each side of the equation. -5.4 + 5.4 + r = -6.720119047 + 5.4 Combine like terms: -5.4 + 5.4 = 0.0 0.0 + r = -6.720119047 + 5.4 r = -6.720119047 + 5.4 Combine like terms: -6.720119047 + 5.4 = -1.320119047 r = -1.320119047 Simplifying r = -1.320119047

Solution

The solution to the problem is based on the solutions from the subproblems. r = {12.120119047, -1.320119047}

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