Answer:
y = 2^-x
Explanation:
The graph appears to be a decaying function with a horizontal asymptote of 0. This matches an exponential function with a negative exponent.
y = a·b^-x
The y-intercept is 1, so the function multiplier is 1.
The value at x=-1 is 2, so the base of the exponent could be 2. (at x=-2, the value is 4, confirming this choice)
The function appears to be ...
y = 2^-x