What happens to a function multiplied by - 1

Its graph is reflected over the x-axis.

Step-by-step explanation:

Multiplying a function by a value gives it a vertical scale factor of that value. When the value is negative, the function's graph is reflected over the x-axis (as well as being scaled).

Multiplying a function by - 1 reflects its graph over the x-axis.

The sign becomes flipped.

If it's a negative it becomes a positive, if it's a positive then it becomes a negative.