18=n-3(n^2-3n)

Solution for 18=n-3(n^2-3n) equation:

Simplifying
18 = n + -3(n2 + -3n)

Reorder the terms:
18 = n + -3(-3n + n2)
18 = n + (-3n * -3 + n2 * -3)
18 = n + (9n + -3n2)

Combine like terms: n + 9n = 10n
18 = 10n + -3n2

Solving
18 = 10n + -3n2

Solving for variable 'n'.

Reorder the terms:
18 + -10n + 3n2 = 10n + -10n + -3n2 + 3n2

Combine like terms: 10n + -10n = 0
18 + -10n + 3n2 = 0 + -3n2 + 3n2
18 + -10n + 3n2 = -3n2 + 3n2

Combine like terms: -3n2 + 3n2 = 0
18 + -10n + 3n2 = 0

Begin completing the square.  Divide all terms by
3 the coefficient of the squared term: 

Divide each side by '3'.
6 + -3.333333333n + n2 = 0

Move the constant term to the right:

Add '-6' to each side of the equation.
6 + -3.333333333n + -6 + n2 = 0 + -6

Reorder the terms:
6 + -6 + -3.333333333n + n2 = 0 + -6

Combine like terms: 6 + -6 = 0
0 + -3.333333333n + n2 = 0 + -6
-3.333333333n + n2 = 0 + -6

Combine like terms: 0 + -6 = -6
-3.333333333n + n2 = -6

The n term is -3.333333333n.  Take half its coefficient (-1.666666667).
Square it (2.777777779) and add it to both sides.

Add '2.777777779' to each side of the equation.
-3.333333333n + 2.777777779 + n2 = -6 + 2.777777779

Reorder the terms:
2.777777779 + -3.333333333n + n2 = -6 + 2.777777779

Combine like terms: -6 + 2.777777779 = -3.222222221
2.777777779 + -3.333333333n + n2 = -3.222222221

Factor a perfect square on the left side:
(n + -1.666666667)(n + -1.666666667) = -3.222222221

Can't calculate square root of the right side.

The solution to this equation could not be determined.