LA to Vegas, graphically

Given the magnitudes and angles of the Δr vectors from San Diego to Los Angeles and from Los Angeles to Las Vegas, find the magnitude and angle of the Δr vector from San Diego to Las Vegas.

Using a protractor and a ruler, we make a careful scale drawing, as shown in the figure. A scale of 1 cm ! 100 km was chosen for this solution. With a ruler, we measure the distance from San Diego to Las Vegas to be 3.8 cm, which corresponds to 380 km. With a protractor, we measure the angle θ to be 71 °.