Hi, I have 2 problems I do not understand; could anyone explain what exactly is meant by u1 and d? and how to solve for the said variables?

Thanks!

1-A sequence is defined by

Un=(71-7n)/2

Find U1 and d.

Another problem, if you can explain one, I'm sure I can understand the other one.

2- A sequence is defined by Un=3n-2

Find u1 and d.

Oh, and when I wrote Un and U1, I meant U with a subscript of n, and U with a subscript of 1. Sorry, I don't know how to make the subscripts appear.

Thanks in advance!