Question

Express the series using sigma notation. 6 + 9 + 12 + 15.

a
b
c
d

Answer 1

D

Explanation:

Answer 2

Option (d) is correct.

6 + 9 + 12 +15 =
`\sum_(k=1)^(4)(3k+3)`

Explanation:

Consider the given series expansion 6 + 9 + 12 +15.

since we have to write in series form of 3.

We first write each term of given series in term of 3k or 3k+3

6 can be written as 3(2) or 3(1)+3

9 can be written as 3(3) or 3(2)+3

12 can be written as 3(4) or 3(3)+3

15 can be written as 3(5) or 3(4)+3

Thus, we can write the given series as ,

`\sum_(k=2)^(5)3k` or
`\sum_(k=1)^(4)(3k+3)`

Since, we have options to choose.

From the given option (d) matches our result.

So, 6 + 9 + 12 +15 =
`\sum_(k=1)^(4)(3k+3)`