For any set $ A $ we say that two functions $ f,g:A\longrightarrow A $ are similar, if there exists a bijection $ h:A\longrightarrow A $ such that $ f\circ h=h\circ g. $ a) If $ A $ has three elements, construct a finite, arbitrary number functions, having as domain and codomain $ A, $ that are two by two similar, and every other function with the same domain and codomain as the ones determined is similar to, at least, one of them. b) For $ A=\mathbb{R} , $ show that the functions $ \sin $ and $ -\sin $ are similar.