You may want to include a question
Given:
The sequence is
436, 218, 109, 54.5, 27.25,...
To find:
The explicit formula for the given sequence.
Solution:
We have,
436, 218, 109, 54.5, 27.25,...
It is a GP because the two consecutive terms have common ratio.
Here,
First term : a=436
Common ratio : d = 
= 
= 
Now, the explicit formula for a GP is

Where, a is the first term and r is the common ratio.
Putting a=436 and r=0.5, we get

Therefore, the correct option is c.
Answer:
This may not be entirely satisfied proof but you should get the idea.
Proof: Start with 1 = -1.
Then we know that if a= b then a + c = b + c and also a / c = b / c.
So we can add 1 to both sides.
We have 1 + 1 = -1 + 1 ⇒ 2 = 0.
Now divide both sides by 2 and we would have 1 = 0.
Now add both sides by 1. This yields 2 = 1.
Therefore if 1 = -1 then 2 = 1.
QED