Answer:
t1 = 2d.
Step-by-step explanation:
The explicit formula for an arithmetic series is
The nth term tn = t1 + d(n - 1) where t1 = the first term , d = common difference and n = term number.
so t17 = t1 + 17d - d = t1 + 16d
and t5 = t1 + 5d - d = t1 + 4d
So t1 + 16d = 3(t1 + 4d)
2t1 = 16d - 12d = 4d
t1 = 2d (answer).
