Answer:
Option B) ![a_{n} = 2\cdot 4^{n-1}](https://tex.z-dn.net/?f=a_%7Bn%7D%20%3D%202%5Ccdot%204%5E%7Bn-1%7D)
Step-by-step explanation:
The given geometric sequence is
2, 8, 32, 128,....
The general form of a geometric sequence is given by
![a_{n} = a_{1}\cdot r^{n-1}](https://tex.z-dn.net/?f=a_%7Bn%7D%20%3D%20a_%7B1%7D%5Ccdot%20r%5E%7Bn-1%7D)
Where n is the nth term that we want to find out.
a₁ is the first term in the geometric sequence that is 2
r is the common ratio and can found by simply dividing any two consecutive numbers in the sequence,
![r=\frac{8}{2} = 4](https://tex.z-dn.net/?f=r%3D%5Cfrac%7B8%7D%7B2%7D%20%3D%204)
You can try other consecutive numbers too, you will get the same common ratio
![r=\frac{32}{8} = 4](https://tex.z-dn.net/?f=r%3D%5Cfrac%7B32%7D%7B8%7D%20%3D%204)
![r=\frac{128}{32} = 4](https://tex.z-dn.net/?f=r%3D%5Cfrac%7B128%7D%7B32%7D%20%3D%204)
So the common ratio is 4 in this case.
Substitute the value of a₁ and r into the above general equation
![a_{n} = 2\cdot 4^{n-1}](https://tex.z-dn.net/?f=a_%7Bn%7D%20%3D%202%5Ccdot%204%5E%7Bn-1%7D)
This is the general form of the given geometric sequence.
Therefore, the correct option is B
Note: Don't multiply the first term and common ratio otherwise you wont get correct results.
Verification:
![a_{n} = 2\cdot 4^{n-1}](https://tex.z-dn.net/?f=a_%7Bn%7D%20%3D%202%5Ccdot%204%5E%7Bn-1%7D)
Lets find out the 2nd term
Substitute n = 2
![a_{2} = 2\cdot 4^{2-1} = 2\cdot 4^{1} = 2\cdot 4 = 8](https://tex.z-dn.net/?f=a_%7B2%7D%20%3D%202%5Ccdot%204%5E%7B2-1%7D%20%3D%202%5Ccdot%204%5E%7B1%7D%20%3D%202%5Ccdot%204%20%3D%208)
Lets find out the 3rd term
Substitute n = 3
![a_{3} = 2\cdot 4^{3-1} = 2\cdot 4^{2} = 2\cdot 16 = 32](https://tex.z-dn.net/?f=a_%7B3%7D%20%3D%202%5Ccdot%204%5E%7B3-1%7D%20%3D%202%5Ccdot%204%5E%7B2%7D%20%3D%202%5Ccdot%2016%20%3D%2032)
Lets find out the 4th term
Substitute n = 4
![a_{4} = 2\cdot 4^{4-1} = 2\cdot 4^{3} = 2\cdot 64 = 128](https://tex.z-dn.net/?f=a_%7B4%7D%20%3D%202%5Ccdot%204%5E%7B4-1%7D%20%3D%202%5Ccdot%204%5E%7B3%7D%20%3D%202%5Ccdot%2064%20%3D%20128)
Lets find out the 5th term
Substitute n = 5
![a_{5} = 2\cdot 4^{5-1} = 2\cdot 4^{4} = 2\cdot 256 = 512](https://tex.z-dn.net/?f=a_%7B5%7D%20%3D%202%5Ccdot%204%5E%7B5-1%7D%20%3D%202%5Ccdot%204%5E%7B4%7D%20%3D%202%5Ccdot%20256%20%3D%20512)
Hence, we are getting correct results!