(4r-21)(r+5)=-96

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Solution for (4r-21)(r+5)=-96 equation:


Simplifying
(4r + -21)(r + 5) = -96

Reorder the terms:
(-21 + 4r)(r + 5) = -96

Reorder the terms:
(-21 + 4r)(5 + r) = -96

Multiply (-21 + 4r) * (5 + r)
(-21(5 + r) + 4r * (5 + r)) = -96
((5 * -21 + r * -21) + 4r * (5 + r)) = -96
((-105 + -21r) + 4r * (5 + r)) = -96
(-105 + -21r + (5 * 4r + r * 4r)) = -96
(-105 + -21r + (20r + 4r2)) = -96

Combine like terms: -21r + 20r = -1r
(-105 + -1r + 4r2) = -96

Solving
-105 + -1r + 4r2 = -96

Solving for variable 'r'.

Reorder the terms:
-105 + 96 + -1r + 4r2 = -96 + 96

Combine like terms: -105 + 96 = -9
-9 + -1r + 4r2 = -96 + 96

Combine like terms: -96 + 96 = 0
-9 + -1r + 4r2 = 0

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

Divide each side by '4'.
-2.25 + -0.25r + r2 = 0

Move the constant term to the right:

Add '2.25' to each side of the equation.
-2.25 + -0.25r + 2.25 + r2 = 0 + 2.25

Reorder the terms:
-2.25 + 2.25 + -0.25r + r2 = 0 + 2.25

Combine like terms: -2.25 + 2.25 = 0.00
0.00 + -0.25r + r2 = 0 + 2.25
-0.25r + r2 = 0 + 2.25

Combine like terms: 0 + 2.25 = 2.25
-0.25r + r2 = 2.25

The r term is -0.25r.  Take half its coefficient (-0.125).
Square it (0.015625) and add it to both sides.

Add '0.015625' to each side of the equation.
-0.25r + 0.015625 + r2 = 2.25 + 0.015625

Reorder the terms:
0.015625 + -0.25r + r2 = 2.25 + 0.015625

Combine like terms: 2.25 + 0.015625 = 2.265625
0.015625 + -0.25r + r2 = 2.265625

Factor a perfect square on the left side:
(r + -0.125)(r + -0.125) = 2.265625

Calculate the square root of the right side: 1.505199322

Break this problem into two subproblems by setting 
(r + -0.125) equal to 1.505199322 and -1.505199322.

Subproblem 1

r + -0.125 = 1.505199322 Simplifying r + -0.125 = 1.505199322 Reorder the terms: -0.125 + r = 1.505199322 Solving -0.125 + r = 1.505199322 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.125' to each side of the equation. -0.125 + 0.125 + r = 1.505199322 + 0.125 Combine like terms: -0.125 + 0.125 = 0.000 0.000 + r = 1.505199322 + 0.125 r = 1.505199322 + 0.125 Combine like terms: 1.505199322 + 0.125 = 1.630199322 r = 1.630199322 Simplifying r = 1.630199322

Subproblem 2

r + -0.125 = -1.505199322 Simplifying r + -0.125 = -1.505199322 Reorder the terms: -0.125 + r = -1.505199322 Solving -0.125 + r = -1.505199322 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.125' to each side of the equation. -0.125 + 0.125 + r = -1.505199322 + 0.125 Combine like terms: -0.125 + 0.125 = 0.000 0.000 + r = -1.505199322 + 0.125 r = -1.505199322 + 0.125 Combine like terms: -1.505199322 + 0.125 = -1.380199322 r = -1.380199322 Simplifying r = -1.380199322

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.630199322, -1.380199322}

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