Since lines l1 and l2 are parallel, they have the same slope. Call that
slope m. Since the slopes sum to less than 1
m + m < 1
2m < 1
m < 1/2
Thus, lines l1 and l2 each have the same slope that is less than 1/2.
A line perpendicular to those lines would have a negative reciprocal slope. However,
there isn’t much more you can do here. Lines l1 and l2 could have slopes of 1/4(in which case a perpendicular line would have slope = –4) or slopes of –
100 (in which case a perpendicular line would have slope = 1/100). Thus, the
slope of the perpendicular line could be less than or greater than –1/2 .