If f(x)=ax+b and with and real, what is the value of ?
f(x) = ax + b
x = a*f^-1(x) + b
f^-1(x) = (1/a) * x - b/a
so you get 1/a = b, -b/a = a
because -b/a = a, b = -a^2
Only solution is a = -1, b = -1.
so a + b = -2.
