Answer: Multiplied by -1
Example:
Let's say we had the linear function y = 2x+5
Reflecting this over the y axis means we replace every x with -x and simplify
y = 2x+5 becomes y = 2(-x)+5 and that simplifies to y = -2x+5
The y intercept stays the same the whole time. This is because the y intercept is on the mirror line of the y axis. Stuff on the mirror line does not move.
Notice the jump from the old slope (2) to the new slope (-2) has us multiply by -1.
