Chapter 2 - Force Vectors - Section 2.8 - Force Vector Directed Along a Line - Problems - Page 65: 86

$r_{AB} = 397 mm$

The coordinates for Point A are: $A(-150 \cos 30°, -150 \sin 30°)\ mm$ The coordinates for Point B are: $B(300)\ mm$ Then: $r_{AB} = [0 - (-150 \cos 30°)] i + [300 - (-150 \sin 30°)] j = [130 i + 375 j]\ mm$ We calculate the magnitude: $r_{AB} =\sqrt{130^2 + 375^2} = 397\ mm$