n-21=n*n

Solution for n-21=n*n equation:

Simplifying
n + -21 = n * n

Reorder the terms:
-21 + n = n * n

Multiply n * n
-21 + n = n2

Solving
-21 + n = n2

Solving for variable 'n'.

Combine like terms: n2 + -1n2 = 0
-21 + n + -1n2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
21 + -1n + n2 = 0

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -1n + -21 + n2 = 0 + -21

Reorder the terms:
21 + -21 + -1n + n2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -1n + n2 = 0 + -21
-1n + n2 = 0 + -21

Combine like terms: 0 + -21 = -21
-1n + n2 = -21

The n term is n.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1n + 0.25 + n2 = -21 + 0.25

Reorder the terms:
0.25 + -1n + n2 = -21 + 0.25

Combine like terms: -21 + 0.25 = -20.75
0.25 + -1n + n2 = -20.75

Factor a perfect square on the left side:
(n + 0.5)(n + 0.5) = -20.75

Can't calculate square root of the right side.

The solution to this equation could not be determined.