4r^2-16r-20=-5

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Solution for 4r^2-16r-20=-5 equation:


Simplifying
4r2 + -16r + -20 = -5

Reorder the terms:
-20 + -16r + 4r2 = -5

Solving
-20 + -16r + 4r2 = -5

Solving for variable 'r'.

Reorder the terms:
-20 + 5 + -16r + 4r2 = -5 + 5

Combine like terms: -20 + 5 = -15
-15 + -16r + 4r2 = -5 + 5

Combine like terms: -5 + 5 = 0
-15 + -16r + 4r2 = 0

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

Divide each side by '4'.
-3.75 + -4r + r2 = 0

Move the constant term to the right:

Add '3.75' to each side of the equation.
-3.75 + -4r + 3.75 + r2 = 0 + 3.75

Reorder the terms:
-3.75 + 3.75 + -4r + r2 = 0 + 3.75

Combine like terms: -3.75 + 3.75 = 0.00
0.00 + -4r + r2 = 0 + 3.75
-4r + r2 = 0 + 3.75

Combine like terms: 0 + 3.75 = 3.75
-4r + r2 = 3.75

The r term is -4r.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4r + 4 + r2 = 3.75 + 4

Reorder the terms:
4 + -4r + r2 = 3.75 + 4

Combine like terms: 3.75 + 4 = 7.75
4 + -4r + r2 = 7.75

Factor a perfect square on the left side:
(r + -2)(r + -2) = 7.75

Calculate the square root of the right side: 2.783882181

Break this problem into two subproblems by setting 
(r + -2) equal to 2.783882181 and -2.783882181.

Subproblem 1

r + -2 = 2.783882181 Simplifying r + -2 = 2.783882181 Reorder the terms: -2 + r = 2.783882181 Solving -2 + r = 2.783882181 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + r = 2.783882181 + 2 Combine like terms: -2 + 2 = 0 0 + r = 2.783882181 + 2 r = 2.783882181 + 2 Combine like terms: 2.783882181 + 2 = 4.783882181 r = 4.783882181 Simplifying r = 4.783882181

Subproblem 2

r + -2 = -2.783882181 Simplifying r + -2 = -2.783882181 Reorder the terms: -2 + r = -2.783882181 Solving -2 + r = -2.783882181 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + r = -2.783882181 + 2 Combine like terms: -2 + 2 = 0 0 + r = -2.783882181 + 2 r = -2.783882181 + 2 Combine like terms: -2.783882181 + 2 = -0.783882181 r = -0.783882181 Simplifying r = -0.783882181

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4.783882181, -0.783882181}

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