Question

Which summation formula represents the series below?
1 + 2 + 6 + 24

Answer 1

Option a: ∑⁵(n−1)! is the correct answer.

n=²

Explanation:

Option a: ∑n=25(n−1)

By substituting the values of n and expanding the summation, we have,

(2−1)!+(3−1)!+(4−1)!+(5−1)!

Subtracting, we have,

1!+2!+3!+4!

Expanding the factorial,

1+(2∗1)+(3∗2∗1)+(4∗3∗2∗1)

Simplifying, we get,

1+2+6+24

Thus, the summation ∑⁵ (n−1)! represents the

n=2

series 1+2+6+24

Hence, Option a is the correct answer.

Answer 2

First one is the answer of the question u asked