Question

Sum of the first 9 terms of an arithmetic sequence is 180 and first term −20.
a) What is its fifth term?
b) What is its common difference?​

Answer 1

Step-by-step explanation:

$s_n = \frac{n}{2} (1 \: term \: + last \: term) \\ \\ 180 = \frac{9}{2} ( - 20 + last \: term) \\ \\ 60 = last \: term \\ \\ 5th \: term = 20 \\ \\ difference = 10$

-20,-10,0,10,20,30,40,50,60