r^2+4r-56=0

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Solution for r^2+4r-56=0 equation:


Simplifying
r2 + 4r + -56 = 0

Reorder the terms:
-56 + 4r + r2 = 0

Solving
-56 + 4r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '56' to each side of the equation.
-56 + 4r + 56 + r2 = 0 + 56

Reorder the terms:
-56 + 56 + 4r + r2 = 0 + 56

Combine like terms: -56 + 56 = 0
0 + 4r + r2 = 0 + 56
4r + r2 = 0 + 56

Combine like terms: 0 + 56 = 56
4r + r2 = 56

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 = 56 + 4

Reorder the terms:
4 + 4r + r2 = 56 + 4

Combine like terms: 56 + 4 = 60
4 + 4r + r2 = 60

Factor a perfect square on the left side:
(r + 2)(r + 2) = 60

Calculate the square root of the right side: 7.745966692

Break this problem into two subproblems by setting 
(r + 2) equal to 7.745966692 and -7.745966692.

Subproblem 1

r + 2 = 7.745966692 Simplifying r + 2 = 7.745966692 Reorder the terms: 2 + r = 7.745966692 Solving 2 + r = 7.745966692 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 = 7.745966692 + -2 Combine like terms: 2 + -2 = 0 0 + r = 7.745966692 + -2 r = 7.745966692 + -2 Combine like terms: 7.745966692 + -2 = 5.745966692 r = 5.745966692 Simplifying r = 5.745966692

Subproblem 2

r + 2 = -7.745966692 Simplifying r + 2 = -7.745966692 Reorder the terms: 2 + r = -7.745966692 Solving 2 + r = -7.745966692 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 = -7.745966692 + -2 Combine like terms: 2 + -2 = 0 0 + r = -7.745966692 + -2 r = -7.745966692 + -2 Combine like terms: -7.745966692 + -2 = -9.745966692 r = -9.745966692 Simplifying r = -9.745966692

Solution

The solution to the problem is based on the solutions from the subproblems. r = {5.745966692, -9.745966692}

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