Answer: (5,5)
Explanation:
The perpendicular to y=x has slope -1, and thus the equation of the perpendicular from (1,9) is
.
Finding the point where they intersect, since both equations are set equal to y, we know that -x+10=x, and thus x=5.
If x=5, then y=5 as well.
So, F has coordinates (5,5).