# What is the domain of the function: {(1, 2); (2, 4); (3, 6); (4, 8)}?

$\left\{1 , 2 , 3 , 4\right\}$
The first components are Xs and the second ones are Ys, so domain are Xs and: ${D}_{f} = \left\{1 , 2 , 3 , 4\right\}$ where ${D}_{f}$ is a domain set.