Answer:
See below.
Step-by-step explanation:
f(x + 3) = f(x) + f(5) (Given) so:
f(2 + 3) = f(2) + f(5)
and f(2) = f(2 + 3) - f(5)
= f(5) - f(5) = 0.
f(-1) = f(-1 +3) - f(5)
= f(2) - f(5)
= f(-3)
So - f(-1) = f(3)
Also:
f(5) = f(x + 3) - f(x)
= f(x + 3 - x)
= f(3).
But f(3) = -f(-1) ( shown above),
So f(5) = -f(-1).
