Respuesta :

f(x) = 9x^3 + 2x^2 - 5x + 4 --------> 9x^3 + 2x^2 - 5x + 4
g(x) = - (5x^3 - 7x + 4) --------> - 5x^3 + 7x - 4
4x^3 + 2x^2 + 2x ---------> 0

I hope this helps you out because I just spent a lot of time figuring it out myself ad typing it out.
kenziejrocks
I hope it doesn't look too messy:

(x)=9x^3+2x^2-5x+4 and g(x)=5x^3-7x+4 
so, by DEFINITION : 
(f-g)(x) = f(x) - g(x) 
= (9x^3 + 2x^2 - 5x + 4) - (5x^3 -7x + 4) 
= 9x^3 + 2x^2 - 5x + 4 - 5x^3 + 7x - 4 <--- sign rule 
= 4x^3 + 2x^2 + 2x