Explanation:
The slope of a line connecting two points is:
m = (y₂ − y₁) / (x₂ − x₁)
The slope of line 1 is:
m = (4 − 0) / (7 − 1)
m = 2/3
The slope of line 2 is:
m = (6 − 0) / (3 − 7)
m = -3/2
Parallel lines have equal slopes.
Perpendicular lines have opposite inverse slopes.
2/3 and -3/2 are opposite inverses, so the lines are perpendicular.