Finding the nth term of a linear sequence (Two Key examples: 5n+3 and -4n+19)

This video shows how to find a linear sequence in the form an+b and also -an+b
It shows how the 1st difference is always the number next to n (coefficient).
It also explains how a+b always add to make the first term
In the first example, the sequence goes up by 5 and so is of the form 5n+3
In the second example it does down by 4 and so is of the form -4n+19