Given f={(1,a),(2,c),(4,d),(3,b)} and g−1={(2,a),(4,b),(1,c),(3,d)}.
Then we have f−1={(a,1),(c,2),(d,4),(b,3)} and g={(a,2),(b,4),(c,1),(d,3)}.
Now gof={(1,2),(2,1),(4,3),(3,4)}⇒(gof)−1={(2,1),(1,2),(3,4),(4,3)}......(1).
Again f−1og−1={(2,1),(4,3),(1,2),(3,4)}={(2,1),(1,2),(3,4),(4,3)}........(2).
From (1) and (2) we have (gof)−1=f−1og−1,