bjr
f(x) = x + 2x = x * x + x * 2 = x (x + 2)
g(x) = 3 (x+5) + (x+5) (2x-4)
= (x+5) (3 + (2x-4))
= (x+5) (2x - 1)
h(x) = (x-1) (x+1) - (x-1) (x+2)
= (x-1) (x+1 - (x+2))
= (x-1) (x + 1 - x - 2)
= (x-1) * (-1) = - (x-1)
et I(x) = (x+5) (x+5) - 3 (x+5) = (x+5) (x+5 - 3) = (x+5) (x+2)