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
