Areas of Combined Polygons
Grade 8 math lesson on calculating the total area of combined or composite polygons by breaking them into simpler shapes. Students learn to decompose irregular figures into rectangles, triangles, and other polygons to find total area.
Key Concepts
New Concept This course introduces foundational math skills, showing how to break down complex problems into simpler, manageable steps. Mastering basics prepares you for advanced challenges. What’s next Next, you’ll apply this strategy in worked examples, learning to calculate the area of combined polygons by dividing or subtracting simpler shapes.
Common Questions
How do you find the area of a combined polygon?
To find the area of a composite figure, decompose it into simpler shapes (rectangles, triangles, trapezoids). Calculate the area of each simple shape separately, then add all the areas together.
What shapes can you break a composite figure into?
Most composite figures can be decomposed into rectangles (area = length x width), triangles (area = 1/2 base x height), circles or semicircles (area = pi r squared), or trapezoids (area = (b1+b2)/2 x height).
How do you find a missing dimension when calculating area of combined shapes?
Use the given measurements to calculate missing dimensions. If you know the total length and one partial length, subtract to find the other. Label all dimensions clearly before calculating.
How do you subtract areas to find combined polygon area?
Sometimes it is easier to calculate the area of the whole shape and subtract the cutout area. For example, a rectangle with a triangular notch cut out: area = rectangle area minus triangle area.