Question

In an AP 9 term of five terms 4 term and 7 term is 17.Find the sum of first 20 terms..​

Answer 1

Step-by-step explanation:

Here,a=5,d= (9-5) =4 and n=23

Now,s Sn=n2×{2a+(n−1)×d}Sn=n2×{2a+(n-1)×d}

S23=232×{2×5+(23−1)×4}S23=232×{2×5+(23-1)×4}

=(232×98)=1127=(232×98)=1127

Hence, the sum of 23 terms of the given AP is 1127.