x(x+2)=399

Solution for x(x+2)=399 equation:

Simplifying
x(x + 2) = 399

Reorder the terms:
x(2 + x) = 399
(2 * x + x * x) = 399
(2x + x2) = 399

Solving
2x + x2 = 399

Solving for variable 'x'.

Reorder the terms:
-399 + 2x + x2 = 399 + -399

Combine like terms: 399 + -399 = 0
-399 + 2x + x2 = 0

Factor a trinomial.
(-21 + -1x)(19 + -1x) = 0

Subproblem 1
Set the factor '(-21 + -1x)' equal to zero and attempt to solve:

Simplifying
-21 + -1x = 0

Solving
-21 + -1x = 0

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

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

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

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

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

Simplifying
x = -21
Subproblem 2
Set the factor '(19 + -1x)' equal to zero and attempt to solve:

Simplifying
19 + -1x = 0

Solving
19 + -1x = 0

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

Add '-19' to each side of the equation.
19 + -19 + -1x = 0 + -19

Combine like terms: 19 + -19 = 0
0 + -1x = 0 + -19
-1x = 0 + -19

Combine like terms: 0 + -19 = -19
-1x = -19

Divide each side by '-1'.
x = 19

Simplifying
x = 19
Solution
x = {-21, 19}