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Area of Triangles & Quadrilaterals (Using Formulas)
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What you will learn from this videoWhat you will learn
- How to find the area of any triangle using a formula.
- How to find the area of quadrilaterals like parallelograms and trapezoids using formulas.
- And we'll see how this knowledge can help us take care of animals, make stickers, and even go camping.
- Discussion Questions
Before Video
What is area? How is it measured? How is it different from perimeter?ANSWERArea is the amount of space inside a shape. Area is measured using square units. Perimeter is the distance around a shape and is measured in units.
48 sq. cm.
Kamal is not correct. The area of this rectangle is 6 cm × 5 cm = 30 sq. cm. It looks like Kamal found the perimeter instead of the area.
The area of a triangle is half the area of a rectangle with the same base and height.
I can divide the shape into one or more rectangles and right triangles. I can calculate the area of each sub-shape and then add the areas together to find the total area.
After Video
A triangle has base length 18 inches and height 6 inches. What formula can help you find the area of this triangle? Find the area.ANSWERThe formula is A=[ggfrac]1/2[/ggfrac]bh. The area of this triangle is 54 sq. in.
The formula is A = bh. The area of the parallelogram is 15 sq. m.
The formula is A=[ggfrac]1/2[/ggfrac](b1+b2)h. The area is 73.5 sq. cm.
Answer will vary. Students may discuss how a non-right triangle can be divided into two right triangles and that makes the same formula. They may discuss how a parallelogram can be transformed into a rectangle.
No, Jasmine is not correct. She multiplied the base (6 units) by the length of one of the sides (4.5 units). She should have multiplied the base (6 units) by the height (4 units). 6 × 4 = 24. The correct answer is 24 square units.
- Vocabulary
- Area DEFINE
The amount of space inside a 2D shape.
- Triangle DEFINE
A figure with 3 sides.
- Formula DEFINE
A rule written with mathematical symbols that connects two or more quantities with an equal sign.
- Quadrilateral DEFINE
A figure with 4 sides.
- Parallelogram DEFINE
A figure with 4 sides and opposite sides parallel.
- Trapezoid DEFINE
A figure with 4 sides and at least one pair of parallel sides.
- Square units DEFINE
A square with side length 1 unit that is used to measure the area of a shape.
- Decompose DEFINE
Break into parts. For example, decompose a parallelogram into a rectangle and two triangles.
- Base DEFINE
One of the measurements of a figure used to find area.
- Height DEFINE
One of the measurements of a figure used to find area.
- Area DEFINE
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide
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