Question:
Which summation formula represents the series below? 1 + 2 + 6 + 24
(a) ![\sum_{n=2}^{5}(n-1) !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D2%7D%5E%7B5%7D%28n-1%29%20%21)
(b) ![\sum_{n=0}^{3} n !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D0%7D%5E%7B3%7D%20n%20%21)
(c) ![\sum_{n=1}^{4}(n+1) !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D1%7D%5E%7B4%7D%28n%2B1%29%20%21)
(d) ![\sum_{n=2}^{5} n !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D2%7D%5E%7B5%7D%20n%20%21)
Answer:
Option a:
is the correct answer.
Explanation:
Option a: ![\sum_{n=2}^{5}(n-1) !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D2%7D%5E%7B5%7D%28n-1%29%20%21)
By substituting the values of n and expanding the summation, we have,
![(2-1) !+(3-1) !+(4-1) !+(5-1) !](https://tex.z-dn.net/?f=%282-1%29%20%21%2B%283-1%29%20%21%2B%284-1%29%20%21%2B%285-1%29%20%21)
Subtracting, we have,
![1 !+2!+3 !+4 !](https://tex.z-dn.net/?f=1%20%21%2B2%21%2B3%20%21%2B4%20%21)
Expanding the factorial,
![1+(2*1)+(3*2*1)+(4*3*2*1)](https://tex.z-dn.net/?f=1%2B%282%2A1%29%2B%283%2A2%2A1%29%2B%284%2A3%2A2%2A1%29)
Simplifying, we get,
![1+2+6+24](https://tex.z-dn.net/?f=1%2B2%2B6%2B24)
Thus, the summation
represents the series ![1+2+6+24](https://tex.z-dn.net/?f=1%2B2%2B6%2B24)
Hence, Option a is the correct answer.
Option b: ![\sum_{n=0}^{3} n !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D0%7D%5E%7B3%7D%20n%20%21)
By substituting the values of n and expanding the summation, we have,
![0!+1!+2!+3!](https://tex.z-dn.net/?f=0%21%2B1%21%2B2%21%2B3%21)
Expanding the factorial,
![0+1+(2*1)+(3*2*1)](https://tex.z-dn.net/?f=0%2B1%2B%282%2A1%29%2B%283%2A2%2A1%29)
Simplifying, we get,
![0+1+2+6](https://tex.z-dn.net/?f=0%2B1%2B2%2B6)
Thus, the summation
does not represents the series ![1+2+6+24](https://tex.z-dn.net/?f=1%2B2%2B6%2B24)
Hence, Option b is not the correct answer.
Option c: ![\sum_{n=1}^{4}(n+1) !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D1%7D%5E%7B4%7D%28n%2B1%29%20%21)
By substituting the values of n and expanding the summation, we have,
![(1+1) !+(2+1) !+(3+1) !+(4+1) !](https://tex.z-dn.net/?f=%281%2B1%29%20%21%2B%282%2B1%29%20%21%2B%283%2B1%29%20%21%2B%284%2B1%29%20%21)
Adding, we have,
![2!+3!+4!+5!](https://tex.z-dn.net/?f=2%21%2B3%21%2B4%21%2B5%21)
Expanding the factorial,
![(2*1)+(3*2*1)+(4*3*2*1)+(5*4*3*2*1)](https://tex.z-dn.net/?f=%282%2A1%29%2B%283%2A2%2A1%29%2B%284%2A3%2A2%2A1%29%2B%285%2A4%2A3%2A2%2A1%29)
Simplifying, we get,
![2+6+24+120](https://tex.z-dn.net/?f=2%2B6%2B24%2B120)
Thus, the summation
does not represents the series ![1+2+6+24](https://tex.z-dn.net/?f=1%2B2%2B6%2B24)
Hence, Option c is not the correct answer.
Option d: ![\sum_{n=2}^{5} n !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D2%7D%5E%7B5%7D%20n%20%21)
By substituting the values of n and expanding the summation, we have,
![2!+3!+4!+5!](https://tex.z-dn.net/?f=2%21%2B3%21%2B4%21%2B5%21)
Expanding the factorial,
![(2*1)+(3*2*1)+(4*3*2*1)+(5*4*3*2*1)](https://tex.z-dn.net/?f=%282%2A1%29%2B%283%2A2%2A1%29%2B%284%2A3%2A2%2A1%29%2B%285%2A4%2A3%2A2%2A1%29)
Simplifying, we get,
![2+6+24+120](https://tex.z-dn.net/?f=2%2B6%2B24%2B120)
Thus, the summation
does not represents the series ![1+2+6+24](https://tex.z-dn.net/?f=1%2B2%2B6%2B24)
Hence, Option d is not the correct answer.
Hence, the correct answer is Option a: ![\sum_{n=2}^{5}(n-1) !](https://tex.z-dn.net/?f=%5Csum_%7Bn%3D2%7D%5E%7B5%7D%28n-1%29%20%21)