Respuesta :

x^2 + 42x + 441

x^2 - 18x + 81
altavistard
Let's actually complete the square for  x^2 + 42x + c ...

x^2 + 42 + (42/2)^2 - (42/2)^2 
becomes
(x+21)^2 - 21/2 (answer)

alternatively,    (x+21)^2 - 10.5