(r-3)(r+15)=4

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Solution for (r-3)(r+15)=4 equation:


Simplifying
(r + -3)(r + 15) = 4

Reorder the terms:
(-3 + r)(r + 15) = 4

Reorder the terms:
(-3 + r)(15 + r) = 4

Multiply (-3 + r) * (15 + r)
(-3(15 + r) + r(15 + r)) = 4
((15 * -3 + r * -3) + r(15 + r)) = 4
((-45 + -3r) + r(15 + r)) = 4
(-45 + -3r + (15 * r + r * r)) = 4
(-45 + -3r + (15r + r2)) = 4

Combine like terms: -3r + 15r = 12r
(-45 + 12r + r2) = 4

Solving
-45 + 12r + r2 = 4

Solving for variable 'r'.

Reorder the terms:
-45 + -4 + 12r + r2 = 4 + -4

Combine like terms: -45 + -4 = -49
-49 + 12r + r2 = 4 + -4

Combine like terms: 4 + -4 = 0
-49 + 12r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '49' to each side of the equation.
-49 + 12r + 49 + r2 = 0 + 49

Reorder the terms:
-49 + 49 + 12r + r2 = 0 + 49

Combine like terms: -49 + 49 = 0
0 + 12r + r2 = 0 + 49
12r + r2 = 0 + 49

Combine like terms: 0 + 49 = 49
12r + r2 = 49

The r term is 12r.  Take half its coefficient (6).
Square it (36) and add it to both sides.

Add '36' to each side of the equation.
12r + 36 + r2 = 49 + 36

Reorder the terms:
36 + 12r + r2 = 49 + 36

Combine like terms: 49 + 36 = 85
36 + 12r + r2 = 85

Factor a perfect square on the left side:
(r + 6)(r + 6) = 85

Calculate the square root of the right side: 9.219544457

Break this problem into two subproblems by setting 
(r + 6) equal to 9.219544457 and -9.219544457.

Subproblem 1

r + 6 = 9.219544457 Simplifying r + 6 = 9.219544457 Reorder the terms: 6 + r = 9.219544457 Solving 6 + r = 9.219544457 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + r = 9.219544457 + -6 Combine like terms: 6 + -6 = 0 0 + r = 9.219544457 + -6 r = 9.219544457 + -6 Combine like terms: 9.219544457 + -6 = 3.219544457 r = 3.219544457 Simplifying r = 3.219544457

Subproblem 2

r + 6 = -9.219544457 Simplifying r + 6 = -9.219544457 Reorder the terms: 6 + r = -9.219544457 Solving 6 + r = -9.219544457 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + r = -9.219544457 + -6 Combine like terms: 6 + -6 = 0 0 + r = -9.219544457 + -6 r = -9.219544457 + -6 Combine like terms: -9.219544457 + -6 = -15.219544457 r = -15.219544457 Simplifying r = -15.219544457

Solution

The solution to the problem is based on the solutions from the subproblems. r = {3.219544457, -15.219544457}

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