Answer:
3
Explanation:
The n th term of an arithmetic sequence is
= a +(n - 1)d
where a is the first term and d the common difference
Given the fifteenth term is - 67, and term 21 is - 97, then
a + 14d = - 67 → (1)
a + 20d = - 97 → (2)
Subtract (1) from (2) term by term
6d = - 30 ( divide both sides by 6 )
d = - 5
Substitute d = - 5 into (1)
a + 14(- 5) = - 67
a - 70 = - 67 ( add 70 to both sides )
a = 3
Thus the first term is 3