Answer:
The expression is and sum of first seven terms is 189.
Step-by-step explanation:
Given : The series 15 + 19 + 23 + . . .
We have to find an expression that defines the series for seven terms .
15 can be written as 11 + 4(1)
19 can be written as 11 + 4(2)
23 can be written as 11 + 4(3)
and so on
Thus, in general for 7 terms,
We can write it as
Thus,
Apply the sum rule,
Consider, ,
Now, Consider
Thus,
Thus, the expression is and sum of first seven terms is 189.