(r-3)(r+20)=0

Solution for (r-3)(r+20)=0 equation:

Simplifying
(r + -3)(r + 20) = 0

Reorder the terms:
(-3 + r)(r + 20) = 0

Reorder the terms:
(-3 + r)(20 + r) = 0

Multiply (-3 + r) * (20 + r)
(-3(20 + r) + r(20 + r)) = 0
((20 * -3 + r * -3) + r(20 + r)) = 0
((-60 + -3r) + r(20 + r)) = 0
(-60 + -3r + (20 * r + r * r)) = 0
(-60 + -3r + (20r + r2)) = 0

Combine like terms: -3r + 20r = 17r
(-60 + 17r + r2) = 0

Solving
-60 + 17r + r2 = 0

Solving for variable 'r'.

Factor a trinomial.
(-20 + -1r)(3 + -1r) = 0

Subproblem 1
Set the factor '(-20 + -1r)' equal to zero and attempt to solve:

Simplifying
-20 + -1r = 0

Solving
-20 + -1r = 0

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

Add '20' to each side of the equation.
-20 + 20 + -1r = 0 + 20

Combine like terms: -20 + 20 = 0
0 + -1r = 0 + 20
-1r = 0 + 20

Combine like terms: 0 + 20 = 20
-1r = 20

Divide each side by '-1'.
r = -20

Simplifying
r = -20
Subproblem 2
Set the factor '(3 + -1r)' equal to zero and attempt to solve:

Simplifying
3 + -1r = 0

Solving
3 + -1r = 0

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

Add '-3' to each side of the equation.
3 + -3 + -1r = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -1r = 0 + -3
-1r = 0 + -3

Combine like terms: 0 + -3 = -3
-1r = -3

Divide each side by '-1'.
r = 3

Simplifying
r = 3
Solution
r = {-20, 3}