Respuesta :

hi

f(x) = (x+9)  (x-4)

if it's cross the  x axis it's means  f(x) = 0

(x+9) (x-4) = 0  means   x+9 = 0  so x = -9  and   x-4 = 0 so x = 4

answers f(x) = 0 for  x = -9 and  x = 4

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