Answer:
Step-by-step explanation:
Givens
a1 = -70
d = -10
an = - 100
Formula
an = a1 + (n - 1)*d
Solution
-100 = -70 + (n - 1)*-10 Remove the brackets.
-100 = - 70 + -10n + 10 Combine
-100 = -60 - 10n Add 60 to both sides
-100+60 = -60+60 - 10n Combine
-40 = - 10n Divide by - 10
-40/-10 = n
n = 4
