Answer:
"the addition of a negative constant"
Explanation:
Please note the following points of functions regarding transformations:
1. If there is a change in amplitude, the function will be compressed/stretched vertically, keeping other variables constant
2. If there is a phase shift, the function would be horizontally transformed
3. If there is a period change, the function would be horizontally compressed/stretched
4. If there is addition of positive/negative constant, the function would shift vertically upward/downwards, respectively.
We can clearly see from the graph that the new function is a vertical downward shift from the original. Hence, looking at the above points, point #4, addition of a negative constant, is correct.