Question

Find the sum of the following AP's (i) 5,7,9,11,...to 18terms

Answer 1

a=5 ,d=2 ,n=18

18th term = a+17d = 5+17(2)

i.e. 18th term or last term is 39

now,

sum of terms = n/2(first term + last term)

i.e. 18/2(5+39)

9(44)= 396

answer is 396