Math Problem Statement

How should we dissect the polygon on the right in order to find its area? Draw straight lines on the shape to show your method of dissection, and then calculate its area.

Solution

To find the area of the polygon, we can dissect it into simpler geometric shapes whose areas are easier to calculate. Here's a step-by-step method to approach this:

  1. Dissecting the Polygon:

    • The polygon is already composed of simple shapes like rectangles and triangles. We can break it down further:
      • A large rectangle on the left with dimensions 10cm×8cm10 \, \text{cm} \times 8 \, \text{cm}.
      • A smaller triangle that is cut out at the bottom-right, with base 4cm4 \, \text{cm} and height 3cm3 \, \text{cm}.
      • Another smaller triangle with base 3cm3 \, \text{cm} and height 3cm3 \, \text{cm} on the top right.
  2. Step 1: Calculate the area of the large rectangle: The large rectangle has dimensions 10cm×8cm10 \, \text{cm} \times 8 \, \text{cm}, so its area is: Area of large rectangle=10×8=80cm2\text{Area of large rectangle} = 10 \times 8 = 80 \, \text{cm}^2

  3. Step 2: Calculate the area of the two triangles:

    • The first triangle (bottom-right) has a base of 4cm4 \, \text{cm} and height 3cm3 \, \text{cm}: Area of triangle 1=12×4×3=6cm2\text{Area of triangle 1} = \frac{1}{2} \times 4 \times 3 = 6 \, \text{cm}^2
    • The second triangle (top-right) has a base of 3cm3 \, \text{cm} and height 3cm3 \, \text{cm}: Area of triangle 2=12×3×3=4.5cm2\text{Area of triangle 2} = \frac{1}{2} \times 3 \times 3 = 4.5 \, \text{cm}^2
  4. Step 3: Subtract the areas of the triangles from the area of the large rectangle: Total area of polygon=80(6+4.5)=8010.5=69.5cm2\text{Total area of polygon} = 80 - (6 + 4.5) = 80 - 10.5 = 69.5 \, \text{cm}^2

Thus, the total area of the polygon is 69.5 cm².

Would you like further clarification on any of the steps? Here are some follow-up questions that might help extend this concept:

  1. How would the dissection change if the triangles had different dimensions?
  2. Can you find other ways to dissect this shape into different simpler polygons?
  3. How do you calculate the area of irregular polygons that cannot be easily dissected?
  4. What is the relationship between the sum of triangle areas and the overall polygon area?
  5. Can you use the coordinate geometry method to calculate the area of this shape?

Tip: When dissecting shapes, always try to break them down into known polygons like rectangles, triangles, or squares to simplify the calculation.

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Math Problem Analysis

Mathematical Concepts

Geometry
Area Calculation
Polygon Dissection

Formulas

Area of rectangle: length × width
Area of triangle: 1/2 × base × height

Theorems

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Suitable Grade Level

Grades 6-8