Answer:
D
Step-by-step explanation:
The terms of the sequence
400, 200, 100, 50, ...
These are the terms of a geometric sequence with n th term
[tex]a_{n}[/tex] = a[tex](r)^{n-1}[/tex]
where a is the first term and r the common ratio
r = [tex]\frac{200}{400}[/tex] = [tex]\frac{100}{200}[/tex] = [tex]\frac{1}{2}[/tex]
The first term a = 400, hence
y = 400[tex](\frac{1}{2}) ^{x-1}[/tex] → D
