Which expression defines the given series for seven terms?

15 + 19 + 23 + . .

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.

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