0=r(r+4)

Solution for 0=r(r+4) equation:

Simplifying
0 = r(r + 4)

Reorder the terms:
0 = r(4 + r)
0 = (4 * r + r * r)
0 = (4r + r2)

Solving
0 = 4r + r2

Solving for variable 'r'.
Remove the zero:
-4r + -1r2 = 4r + r2 + -4r + -1r2

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

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

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

Factor out the Greatest Common Factor (GCF), '-1r'.
-1r(4 + r) = 0

Ignore the factor -1.
Subproblem 1
Set the factor 'r' equal to zero and attempt to solve:

Simplifying
r = 0

Solving
r = 0

Move all terms containing r to the left, all other terms to the right.

Simplifying
r = 0
Subproblem 2
Set the factor '(4 + r)' equal to zero and attempt to solve:

Simplifying
4 + r = 0

Solving
4 + r = 0

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 = 0 + -4

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

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

Simplifying
r = -4
Solution
r = {0, -4}