Question

What is the domain of the relation {(3, 4), (1, 3), (1, 4), (5, 2)}?

Answer 1

Domain  = {3,1,5}.
If we look at the relation we find that the first numbers are 3,1,1 and 5.
And we know that the first number of a relation is its domain.

Answer 2

Domain of a relation is knows as it's x-coordinates. So, Here, 
Domain = {3, 1, 1, 5}

Hope it helped!!