Step-by-step explanation:
arithmetic sequence means that every new term is created by adding a certain constant to the previous term.
we clearly see, that constant here is -9.
we start with 26.
a1 = 26
a2 = a1 - 9 = 26 - 9 = 17
a3 = a2 - 9 = a1 - 2×9 = 26 - 18 = 8
so, we see
an = an-1 - 9 = a1 - (n-1)×9 = 26 - (n-1)×9
a59 = 26 - 58×9 = -496
