Question

sum of the first 10 terms of an arithmetic sequence is 155. What is the sum of 5th and 6th terms. If the 2nd term is 5, what is the 9th term?​

Answer 1

Answer:

Step-by-step explanation:

s_n=n/2(2a+(n-1)d)

155=5(2a+9d)

s_(n-1)=9/2(2a+8d)

a_n=10/2(2a+9d) - {9/2(2a+8d)}

a_n=a+9d

a+d=5

then

155/5=2a+9d

31=2a+9d

31-5=2a+9d-a-d

16=a+8d

16-5=a+8d-a-d

11=7d

d=11/7

5-11/7=a

a=24/7