(r-7)(r+5)=20

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Solution for (r-7)(r+5)=20 equation:


Simplifying
(r + -7)(r + 5) = 20

Reorder the terms:
(-7 + r)(r + 5) = 20

Reorder the terms:
(-7 + r)(5 + r) = 20

Multiply (-7 + r) * (5 + r)
(-7(5 + r) + r(5 + r)) = 20
((5 * -7 + r * -7) + r(5 + r)) = 20
((-35 + -7r) + r(5 + r)) = 20
(-35 + -7r + (5 * r + r * r)) = 20
(-35 + -7r + (5r + r2)) = 20

Combine like terms: -7r + 5r = -2r
(-35 + -2r + r2) = 20

Solving
-35 + -2r + r2 = 20

Solving for variable 'r'.

Reorder the terms:
-35 + -20 + -2r + r2 = 20 + -20

Combine like terms: -35 + -20 = -55
-55 + -2r + r2 = 20 + -20

Combine like terms: 20 + -20 = 0
-55 + -2r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '55' to each side of the equation.
-55 + -2r + 55 + r2 = 0 + 55

Reorder the terms:
-55 + 55 + -2r + r2 = 0 + 55

Combine like terms: -55 + 55 = 0
0 + -2r + r2 = 0 + 55
-2r + r2 = 0 + 55

Combine like terms: 0 + 55 = 55
-2r + r2 = 55

The r term is -2r.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2r + 1 + r2 = 55 + 1

Reorder the terms:
1 + -2r + r2 = 55 + 1

Combine like terms: 55 + 1 = 56
1 + -2r + r2 = 56

Factor a perfect square on the left side:
(r + -1)(r + -1) = 56

Calculate the square root of the right side: 7.483314774

Break this problem into two subproblems by setting 
(r + -1) equal to 7.483314774 and -7.483314774.

Subproblem 1

r + -1 = 7.483314774 Simplifying r + -1 = 7.483314774 Reorder the terms: -1 + r = 7.483314774 Solving -1 + r = 7.483314774 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + r = 7.483314774 + 1 Combine like terms: -1 + 1 = 0 0 + r = 7.483314774 + 1 r = 7.483314774 + 1 Combine like terms: 7.483314774 + 1 = 8.483314774 r = 8.483314774 Simplifying r = 8.483314774

Subproblem 2

r + -1 = -7.483314774 Simplifying r + -1 = -7.483314774 Reorder the terms: -1 + r = -7.483314774 Solving -1 + r = -7.483314774 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + r = -7.483314774 + 1 Combine like terms: -1 + 1 = 0 0 + r = -7.483314774 + 1 r = -7.483314774 + 1 Combine like terms: -7.483314774 + 1 = -6.483314774 r = -6.483314774 Simplifying r = -6.483314774

Solution

The solution to the problem is based on the solutions from the subproblems. r = {8.483314774, -6.483314774}

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