If f(x)=ax+bcx+df(x) = \frac{ax+b}{cx+d}f(x)=cx+dax+b and f(f(x))=xf(f(x)) = xf(f(x))=x for all xxx in the domain, which relation must hold between a,b,c,da, b, c, da,b,c,d?
a+d=0a+d = 0a+d=0
a=da=da=d
ad−bc=0ad-bc = 0ad−bc=0
b=cb=cb=c