Math Problem Statement

A gardener marks out a garden plot with poles positioned at specific locations: the first pole is at (0,0), the second pole is 6 feet to the east at (6,0), the third pole is at (4,5), and the fourth pole is at (2,4). Calculate the total area of the garden plot.

Solution

To calculate the total area of the garden plot defined by the poles at (0,0)(0,0), (6,0)(6,0), (4,5)(4,5), and (2,4)(2,4), we can use the shoelace formula, which calculates the area of a polygon given its vertices in order.

Shoelace Formula

If the vertices of the polygon are (x1,y1),(x2,y2),...,(xn,yn)(x_1, y_1), (x_2, y_2), ..., (x_n, y_n), then the area is:

Area=12i=1n1(xiyi+1yixi+1)+(xny1ynx1)\text{Area} = \frac{1}{2} \left| \sum_{i=1}^{n-1} (x_i y_{i+1} - y_i x_{i+1}) + (x_n y_1 - y_n x_1) \right|

Vertices

The given vertices are: (0,0),(6,0),(4,5),(2,4)(0,0), (6,0), (4,5), (2,4) We will arrange them in order and repeat the first vertex at the end: (0,0),(6,0),(4,5),(2,4),(0,0)(0,0), (6,0), (4,5), (2,4), (0,0)

Applying the Formula

We calculate each term in the formula step by step:

  1. x1y2=00=0x_1y_2 = 0 \cdot 0 = 0
  2. x2y3=65=30x_2y_3 = 6 \cdot 5 = 30
  3. x3y4=44=16x_3y_4 = 4 \cdot 4 = 16
  4. x4y1=20=0x_4y_1 = 2 \cdot 0 = 0

Sum of these terms: 0+30+16+0=460 + 30 + 16 + 0 = 46.

Next, calculate the other diagonal terms:

  1. y1x2=06=0y_1x_2 = 0 \cdot 6 = 0
  2. y2x3=04=0y_2x_3 = 0 \cdot 4 = 0
  3. y3x4=52=10y_3x_4 = 5 \cdot 2 = 10
  4. y4x1=40=0y_4x_1 = 4 \cdot 0 = 0

Sum of these terms: 0+0+10+0=100 + 0 + 10 + 0 = 10.

Subtract and Divide

The area is: Area=124610=1236=18square feet.\text{Area} = \frac{1}{2} \left| 46 - 10 \right| = \frac{1}{2} \cdot 36 = 18 \, \text{square feet}.

Final Answer

The total area of the garden plot is:

18square feet\boxed{18 \, \text{square feet}}


Would you like a detailed explanation of any step or further examples? Here are related questions:

  1. What is the shoelace formula and how is it derived?
  2. How do you determine the order of vertices for such problems?
  3. Can you use this method for non-convex polygons?
  4. What are practical applications of the shoelace formula?
  5. What are alternative methods to calculate the area of a polygon?

Tip: Always ensure the vertices are ordered sequentially (clockwise or counterclockwise) before applying the shoelace formula!

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Math Problem Analysis

Mathematical Concepts

Geometry
Polygon Area Calculation

Formulas

Shoelace formula: Area = 1/2 |Σ(x_i * y_(i+1) - y_i * x_(i+1))|

Theorems

Shoelace theorem for polygons

Suitable Grade Level

Grades 9-12