Surjection / Surjective function

In this video we cover the following:
-the definition of a surjection 0:00
-image and preimage interpretation 1:01
-Venn diagram interpretation 1:38

Examples
-identity function on A 2:16
-Absolute value function 3:15
-projection of the plane onto the x-axis 5:01
-sin function 5:58

Preliminary material: