Respuesta :

Answer:

f(x) = (x+10)^2 - 86

Step-by-step explanation:

  1. f(x) = x^2 + 20x - 86
  2. f(x) = x^2 + 20x + 100 - 86 (because (20/2)^2 = 100)
  3. f(x) = (x+10)^2 - 86

Completing the square means you do (b/2)^2 where b is: a^2x + bx + c.