Which is an exponential decay function?
f start bracket x end bracket equals three-fourths start bracket seven-fourths end bracket superscript x
f start bracket x end bracket equals two-third start bracket four-fifths end bracket superscript negative x
f start bracket x end bracket equals three-halves start bracket eight-sevenths end bracket superscript negative x
f start bracket x end bracket equals one-third start bracket negative nine-halves end bracket superscript x

I think this question already have an answer that is answered on this but I will still solve it:
Here is the translation:
f(x)= 3/4 (7/4)^+x
f(x)= 2/3 (4/5)^-x
f(x)= 3/2 (8/7)^-x
f(x)= 1/3 (9/2)^+x

Basically you have to check if each statement is true.
^-x= <
^+x= >

7/4 > 1 is 1.75 > 1, making the statement true. (Positive exponential function)

4/5 < 1 is 0.8 < 1, making it true.
(Positive exponential function)

8/7 > 1 is 1.1428.. < 1, making this statement false and thus a decay exponential function.

9/2 > 1 is 4.5 > 1, making it true.
(Positive exponential function)

The answer is the third option:
f(x)= 3/2 (8/7)^-x

Wow thats alot but it would be the 3 one