Example 6 from Algebra and Trigonometry, 2.1 The Rectangular Coordinate Systems and Graphs

Finding the Distance between Two Locations

Let’s return to the situation introduced at the beginning of this section.

Tracie set out from Elmhurst, IL, to go to Franklin Park. On the way, she made a few stops to do errands. Each stop is indicated by a red dot in Figure 1. Find the total distance that Tracie traveled. Compare this with the distance between her starting and final positions.

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

1
Solution
The first thing we should do is identify ordered pairs to describe each position. If we set the starting position at the origin, we can identify each of the other points by counting units east (right) and north (up) on the grid. For example, the first stop is 1 block east and 1 block north, so it is at $(1, 1) .$ The next stop is 5 blocks to the east, so it is at $(5, 1) .$ After that, she traveled 3 blocks east and 2 blocks north to $(8, 3) .$ Lastly, she traveled 4 blocks north to $(8, 7) .$ We can label these points on the grid as in Figure 15.

Figure 15

Next, we can calculate the distance. Note that each grid unit represents 1,000 feet.
- From her starting location to her first stop at $(1, 1),$ Tracie might have driven north 1,000 feet and then east 1,000 feet, or vice versa. Either way, she drove 2,000 feet to her first stop.
- Her second stop is at $(5, 1) .$ So from $(1, 1)$ to $(5, 1),$ Tracie drove east 4,000 feet.
- Her third stop is at $(8, 3) .$ There are a number of routes from $(5, 1)$ to $(8, 3) .$ Whatever route Tracie decided to use, the distance is the same, as there are no angular streets between the two points. Let’s say she drove east 3,000 feet and then north 2,000 feet for a total of 5,000 feet.
- Tracie’s final stop is at $(8, 7) .$ This is a straight drive north from $(8, 3)$ for a total of 4,000 feet.
Next, we will add the distances listed in Table 3.

From/To Number of Feet Driven

$(0, 0)$ to $(1, 1)$ 2,000

$(1, 1)$ to $(5, 1)$ 4,000

$(5, 1)$ to $(8, 3)$ 5,000

$(8, 3)$ to $(8, 7)$ 4,000

Total 15,000

Table 3

The total distance Tracie drove is 15,000 feet, or 2.84 miles. This is not, however, the actual distance between her starting and ending positions. To find this distance, we can use the distance formula between the points $(0, 0)$ and $(8, 7) .$

$\begin{array}{l} d = \sqrt{{(8 - 0)}^{2} + {(7 - 0)}^{2}} \\ = \sqrt{64 + 49} \\ = \sqrt{113} \\ \approx 10.63 units \end{array}$
At 1,000 feet per grid unit, the distance between Elmhurst, IL, to Franklin Park is 10,630.14 feet, or 2.01 miles. The distance formula results in a shorter calculation because it is based on the hypotenuse of a right triangle, a straight diagonal from the origin to the point $(8, 7) .$ Perhaps you have heard the saying “as the crow flies,” which means the shortest distance between two points because a crow can fly in a straight line even though a person on the ground has to travel a longer distance on existing roadways.

From/To	Number of Feet Driven
$(0, 0)$ to $(1, 1)$	2,000
$(1, 1)$ to $(5, 1)$	4,000
$(5, 1)$ to $(8, 3)$	5,000
$(8, 3)$ to $(8, 7)$	4,000
Total	15,000

How did it go?

From/To	Number of Feet Driven
$(0, 0)$ to $(1, 1)$	2,000
$(1, 1)$ to $(5, 1)$	4,000
$(5, 1)$ to $(8, 3)$	5,000
$(8, 3)$ to $(8, 7)$	4,000
Total	15,000

From/To

Number of Feet Driven

(0, 0)

(1, 1)

2,000

(1, 1)

(5, 1)

4,000

(5, 1)

(8, 3)

5,000

(8, 3)

(8, 7)

4,000

Total

15,000

Solution

Solution