Question

sum of 1st 9 terms of an arithmetic sequence is 45 and the sum of 1st 18 terms is 171
a. what is the sum of the 10nth and 18nth terms
b. what is it's 5th term
c. find its 14nth term
d find the sum of 5th to 14 terms​

Answer 1

Step-by-step explanation:

9/2(2a+8d)=45.........1

18/2(2a+17d)=171.........2

18a+72d=90.......1

18a+153d=171.....2

-81d=--81

d=1

18a+72=90

18a=18

a=1

(b) 1+4*1

5 answer