In Example 5(b), change −1.732 to −0.5774.

Data from Example 5(b)

If a line has a slope of −1.732, we know that tan α = −1.732. Because tan α is negative, α must be a second-quadrant angle. Therefore, using a calculator to show that tan60° = 1.732, we find that α = 180° − 60° = 120°. See Fig. 21.8.

y a = 120 0 m=1 a = 45 m=-1.732 Fig. 21.8 X