(r-2)(r+10)=12

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Solution for (r-2)(r+10)=12 equation:


Simplifying
(r + -2)(r + 10) = 12

Reorder the terms:
(-2 + r)(r + 10) = 12

Reorder the terms:
(-2 + r)(10 + r) = 12

Multiply (-2 + r) * (10 + r)
(-2(10 + r) + r(10 + r)) = 12
((10 * -2 + r * -2) + r(10 + r)) = 12
((-20 + -2r) + r(10 + r)) = 12
(-20 + -2r + (10 * r + r * r)) = 12
(-20 + -2r + (10r + r2)) = 12

Combine like terms: -2r + 10r = 8r
(-20 + 8r + r2) = 12

Solving
-20 + 8r + r2 = 12

Solving for variable 'r'.

Reorder the terms:
-20 + -12 + 8r + r2 = 12 + -12

Combine like terms: -20 + -12 = -32
-32 + 8r + r2 = 12 + -12

Combine like terms: 12 + -12 = 0
-32 + 8r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '32' to each side of the equation.
-32 + 8r + 32 + r2 = 0 + 32

Reorder the terms:
-32 + 32 + 8r + r2 = 0 + 32

Combine like terms: -32 + 32 = 0
0 + 8r + r2 = 0 + 32
8r + r2 = 0 + 32

Combine like terms: 0 + 32 = 32
8r + r2 = 32

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 = 32 + 16

Reorder the terms:
16 + 8r + r2 = 32 + 16

Combine like terms: 32 + 16 = 48
16 + 8r + r2 = 48

Factor a perfect square on the left side:
(r + 4)(r + 4) = 48

Calculate the square root of the right side: 6.92820323

Break this problem into two subproblems by setting 
(r + 4) equal to 6.92820323 and -6.92820323.

Subproblem 1

r + 4 = 6.92820323 Simplifying r + 4 = 6.92820323 Reorder the terms: 4 + r = 6.92820323 Solving 4 + r = 6.92820323 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 = 6.92820323 + -4 Combine like terms: 4 + -4 = 0 0 + r = 6.92820323 + -4 r = 6.92820323 + -4 Combine like terms: 6.92820323 + -4 = 2.92820323 r = 2.92820323 Simplifying r = 2.92820323

Subproblem 2

r + 4 = -6.92820323 Simplifying r + 4 = -6.92820323 Reorder the terms: 4 + r = -6.92820323 Solving 4 + r = -6.92820323 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 = -6.92820323 + -4 Combine like terms: 4 + -4 = 0 0 + r = -6.92820323 + -4 r = -6.92820323 + -4 Combine like terms: -6.92820323 + -4 = -10.92820323 r = -10.92820323 Simplifying r = -10.92820323

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.92820323, -10.92820323}

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