Question

wich expression defines the given series for seven terms? 8+13+18+.......

Answer 1

you're just adding 5 
example
8+5= 13
13+5=18
18+5=23
23+5=28
28+5=33
and so on :)

Answer 2

Answer: a+6d will defines the series for seven terms i.e. 38.

Step-by-step explanation:

Since we have given that

$8+13+18+......$

Here, a = first term = 8

d = common difference is given by

$a_2-a_1\\\\=13-8\\\\=5$

So, we need to find the seven terms:

So, here n = 7

So, it becomes,

$a_7=a+(n-1)d\\\\a_7=8+(7-1)5\\\\a_7=8+6\times 5\\\\a_7=8+30\\\\a_7=38$

Hence, a+6d will defines the series for seven terms i.e. 38.