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Find the area of the pentagon whose vertices are: \((-5,-5),(5,-5),(8,6),(-8,6),\) and (0,12.5)

Short Answer

Expert verified
The area of the pentagon is 89.25 square units.

Step by step solution

01

Understand the Shoelace Theorem

The Shoelace Theorem provides a formula for finding the area of a polygon when the coordinates of its vertices are known. For a pentagon, you must list all vertices in order and repeat the first vertex at the end.
02

List Vertices in Order

Write the coordinates of the vertices in the following order: 1. (-5,-5) 2. (5,-5) 3. (8,6) 4. (-8,6) 5. (0,12.5) 6. Repeating the first vertex: (-5,-5).
03

Set Up the Shoelace Formula

Using the ordered vertices, the Shoelace formula to find the area is:\[\text{Area} = \frac{1}{2} \left| \sum (x_i y_{i+1}) - \sum (y_i x_{i+1}) \right|\]
04

Calculate \(\sum (x_i y_{i+1})\)

For each consecutive pair of vertices, calculate \(x_i \times y_{i+1}\): 1. (-5 \times -5) = 252. (5 \times 6) = 303. (8 \times 6) = 484. (-8 \times 12.5) = -1005. (0 \times -5) = 0.Sum those results: 25 + 30 + 48 - 100 + 0 = 3.
05

Calculate \(\sum (y_i x_{i+1})\)

For each consecutive pair of vertices, calculate \(y_i \times x_{i+1}\): 1. (-5 \times 5) = -252. (-5 \times 8) = -403. (6 \times -8) = -484. (6 \times 0) = 05. (12.5 \times -5) = -62.5.Sum those results: -25 - 40 - 48 + 0 - 62.5 = -175.5.
06

Apply the Shoelace Formula

Subtract the sum from Step 5 from the sum in Step 4 and divide by 2:\[\text{Area} = \frac{1}{2} \left|3 - (-175.5)\right| = \frac{1}{2} \times 178.5 = 89.25\].
07

Conclude with the Area

The area of the pentagon is 89.25 square units.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Area of Polygons
To find the area of polygons like a pentagon, we often use specialized formulas that are applicable when the coordinates of the vertices are known. One popular method is the Shoelace Theorem. This theorem offers a neat, algorithmic approach to calculate the area of a polygon when its vertices are given in a coordinate plane.
The Shoelace Theorem tells us that we need to strategically arrange the coordinates of the vertices. After listing all vertices in sequence, the first vertex should be repeated at the end. This cyclical repetition helps form a seamless calculation matrix.
Next, divide your process into several steps: calculate the sum of specific cross-products of coordinates for the vertices. This process mimics tying shoelaces, hence the name of the theorem. Finally, using subtraction and division by two, you can reveal the area. This method proves incredibly useful for students working in plane geometry who need to handle irregular shapes with precision.
Coordinate Geometry
In coordinate geometry, we explore geometric figures through a plane equipped with a coordinate system. This allows us to pinpoint the exact location of shapes or points and analyze their properties through algebraic equations.
Utilizing coordinate geometry becomes particularly advantageous when dealing with polygons. Each vertex of the polygon is plotted as a point in the coordinate plane, defined by its X and Y coordinates. Understanding the placement of these points assists in visualizing the shape and solving complex calculations, such as finding the area or perimeter.
By leveraging points on this plane, you can practically apply various theorems, like the Shoelace Theorem, mentioned previously. Coordinate geometry not only simplifies calculations but also bridges the gap between algebra and geometry, providing a comprehensive analytical toolset.
Vertices of Polygons
The vertices of a polygon are the points where two sides meet. In mathematical exercises, vertices are often presented as coordinates in a plane, such as \((-5,-5)\) or \(8,6\). Accurately identifying these coordinates is crucial for solving problems related to polygonal shapes.
When vertices of polygons get listed in a specific order, it becomes straightforward to engage with formulas like the Shoelace Theorem. Ensuring that you start and end with the same vertex is key to correctly setting up the calculations. This cyclical path ensures continuity in computation, looping seamlessly back to the initial starting point.
Understanding the placement and order of vertices assists in guaranteeing accuracy, especially in areas involving complex and irregular shapes. Each vertex's pair of X and Y coordinates plays a part in defining the overall size and shape of the polygon, making precise identification paramount in reaching correct conclusions.

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