The graph shows an exponential decay curve that starts from a positive value near $y = 1$ when $x = 0$ and approaches zero as $x$ increases. The curve also drops below zero, heading towards negative infinity as $x$ decreases.

The correct equation for this type of graph is $y = -4^x$. This matches the behavior where the graph reflects the general shape of the exponential growth of $4^x$ but is flipped downward (negative sign).

Thus, the answer is:

$y = -4^x$.

Would you like further details or explanations?

Here are 5 follow-up questions related to this concept:

1. What is the general form of an exponential function?
2. How does the negative sign in an exponential function affect its graph?
3. How does the base of an exponential function affect the growth or decay?
4. How do transformations like reflections and translations affect exponential graphs?
5. What real-world situations can be modeled using exponential decay?

Tip: In exponential functions, a negative base or coefficient causes a reflection of the graph over the x-axis.