Which statement is true about the domain of y = 3(2^-x)? explain.

the domain is all real numbers greater than or equal to 2.
the domain is all real numbers greater than 0
the domain is all real numbers
the domain is all real numbers less than 0

We want to determine the domain of 

any function of the form  is called an "exponential function",
the only condition is that b is positive and different from 1, and a is a nonzero real number.

The domain of such functions is all real numbers.

That is for any x, the expression 3(2^-x) "makes sense".

 The domain is all real numbers