Question

The 3rd term of a linear sequence is -9 and the 8th term is 26.Find the first term and the common difference.

Answer 1

Using our definitions applied to your data:
a+2d = -9
a+7d = 26
subtract them,
5d = 35
d = 7
backsub
a+2d = -9
a + 14 = -9
a = -23