x(5x+21)+18=0

Solution for x(5x+21)+18=0 equation:

Simplifying
x(5x + 21) + 18 = 0

Reorder the terms:
x(21 + 5x) + 18 = 0
(21 * x + 5x * x) + 18 = 0
(21x + 5x2) + 18 = 0

Reorder the terms:
18 + 21x + 5x2 = 0

Solving
18 + 21x + 5x2 = 0

Solving for variable 'x'.

Factor a trinomial.
(3 + x)(6 + 5x) = 0

Subproblem 1
Set the factor '(3 + x)' equal to zero and attempt to solve:

Simplifying
3 + x = 0

Solving
3 + x = 0

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

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

Combine like terms: 3 + -3 = 0
0 + x = 0 + -3
x = 0 + -3

Combine like terms: 0 + -3 = -3
x = -3

Simplifying
x = -3
Subproblem 2
Set the factor '(6 + 5x)' equal to zero and attempt to solve:

Simplifying
6 + 5x = 0

Solving
6 + 5x = 0

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

Add '-6' to each side of the equation.
6 + -6 + 5x = 0 + -6

Combine like terms: 6 + -6 = 0
0 + 5x = 0 + -6
5x = 0 + -6

Combine like terms: 0 + -6 = -6
5x = -6

Divide each side by '5'.
x = -1.2

Simplifying
x = -1.2
Solution
x = {-3, -1.2}