Question 837744
a) Let a = b = 0.
f(0) = f(0) + f(0) --> f(0) = 0


b) Substitute b = a


c) Substitute b = -2a
f(-a) = f(a) + f(-2a)
f(-a) = f(a) + 2f(-a)
Subtract f(-a) from both sides
0 = f(a) + f(-a)
f(-a) = -f(a)