Respuesta :

Answer: (x+4.5)^2-40.25

Step-by-step explanation:

x^2+9x-20=

x^2+9x+4.5^2-4.5^2-20=

x^2+9x+20.25-20.25-20=

(x+4.5)^2-20.25-20=(x+4.5)^2-40.25