(s+18)(s-21)=0

Solution for (s+18)(s-21)=0 equation:

Simplifying
(s + 18)(s + -21) = 0

Reorder the terms:
(18 + s)(s + -21) = 0

Reorder the terms:
(18 + s)(-21 + s) = 0

Multiply (18 + s) * (-21 + s)
(18(-21 + s) + s(-21 + s)) = 0
((-21 * 18 + s * 18) + s(-21 + s)) = 0
((-378 + 18s) + s(-21 + s)) = 0
(-378 + 18s + (-21 * s + s * s)) = 0
(-378 + 18s + (-21s + s2)) = 0

Combine like terms: 18s + -21s = -3s
(-378 + -3s + s2) = 0

Solving
-378 + -3s + s2 = 0

Solving for variable 's'.

Factor a trinomial.
(-18 + -1s)(21 + -1s) = 0

Subproblem 1
Set the factor '(-18 + -1s)' equal to zero and attempt to solve:

Simplifying
-18 + -1s = 0

Solving
-18 + -1s = 0

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

Add '18' to each side of the equation.
-18 + 18 + -1s = 0 + 18

Combine like terms: -18 + 18 = 0
0 + -1s = 0 + 18
-1s = 0 + 18

Combine like terms: 0 + 18 = 18
-1s = 18

Divide each side by '-1'.
s = -18

Simplifying
s = -18
Subproblem 2
Set the factor '(21 + -1s)' equal to zero and attempt to solve:

Simplifying
21 + -1s = 0

Solving
21 + -1s = 0

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

Add '-21' to each side of the equation.
21 + -21 + -1s = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -1s = 0 + -21
-1s = 0 + -21

Combine like terms: 0 + -21 = -21
-1s = -21

Divide each side by '-1'.
s = 21

Simplifying
s = 21
Solution
s = {-18, 21}