function problem?

Let A={2,4,6,8} , B={1,3,5,7}, C={a,b,c,d,e}, the function F:A->C be given
by the rule F={(2,a),(4,b),(6,c),(8,d)} and the function g:B->A be given by
the rule g={(1,2),(3,4),(5,6),(7,8)}

a) find f*g

b) is f onto? explain

c) is g onto? explain

2014-03-14T18:15:47Z

i got I got {(2,1),(4,3),(6,5),(8,7)}
is this right?

2014-03-14T18:20:13Z

b) f is onto because every element on C is mapped to A
c) g is onto because every element on B mapped to A

Randy P2014-03-14T17:28:32Z

Favorite Answer

g = {(1,2), (3, 4), (5,6), (7,8) }.
f*g means replace the second number in each pair by f of that number. For instance in (1,2) you replace 2 by what f maps 2 to, which is a, since f contains the rule (2, a).

So the first pair in f*g is (1, a).
The second is (3, f(4))
And so on.

b) Does every element of C occur in f?
c) Does every element of A occur in g?