Teaching Elementary Students How to Find the Area of a Triangle
Figuring out the area of a triangle is as simple as plugging numbers into a formula. However, teaching children to find the area of a triangle is a little more involved. By the end of the lesson, they should have a firm understanding of the concept of area and why the formulas work. It is important for elementary students to have a solid foundation of basic geometric knowledge. These skills will provide the basis for more advanced mathematics later, as these students apply math into their everyday lives and careers.
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Instructions
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Concept of Area and Formula
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Introduce the definition of area as the space within a flat or two-dimensional object or shape. Ask the children to point out two-dimensional objects within the classroom.
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Discuss how you might use the area of a space or shape in everyday life. For example, explain how they would use the formula to determine the amount of carpet or tile needed to cover a floor or how much wallpaper would be needed for a wall.
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3
Familiarize the children with the concept of area by finding the area of a rectangle. Draw a rectangle and display it on the overhead projector. Label the sides as "Base" and "Height," accordingly. Include only whole squares within the rectangle.
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4
Count the squares aloud with the class to find the area inside the rectangle. Write the formula for the area of a rectangle as "base x height = area." Instruct the children to use the formula to find the area.
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5
Call attention to the fact that the answer acquired by counting the number of squares is the same answer achieved using the formula.
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6
Draw a straight line from one corner of the rectangle to the opposite corner to divide the rectangle in half, creating two congruent triangles.
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Write the formula "(base x height) /2 = area" and instruct the children to copy it on the graph paper in front of them. Discuss the relationship between the area of a rectangle and the area of a triangle.
Parts of a Triangle and Related Terms
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Introduce the parts of a triangle used to determine the area of a triangle, including the base and height.
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Define or review other related terms such as opposite, adjacent, side and angle, with an emphasis on right or perpendicular angles.
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Explain that the height of a triangle is at a right angle to its base. Draw examples of right triangles as well as obtuse and acute triangles.
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Show the class how to use a protractor to distinguish the difference between the different types of angles in each example.
Applyiing the Formula
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Instruct the children to draw a triangle on their graph paper. Specify that the base should begin and end at the line between squares on the graph. Label the base with the letter “B.”
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Tell the class to place the protractor over the triangle so that the base lines up with the bottom edge of the protractor.
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Ask the children to decide if either of the angles adjacent to the base are right angles. If it is a right angle, mark the adjacent side with an “H” for height.
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Teach the children to use their protractors to create a line that will be used as the height when the triangle does not contain a right angle. Label the line with an "H." Help the children identify the height of their own triangles.
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16
Instruct the class to rewrite the formula for the area of a triangle, replacing the letters with the appropriate values for "B" and "H." Solve the equation to find the area and check their answers.
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Encourage the children to draw different types of triangles on their graph paper and find the area for each one. Practice until the children are comfortable with the concept.
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Tips & Warnings
Depending on the children's understanding of the concepts, you may want to wait to introduce acute and obtuse triangles until the class is comfortable finding the area of a right triangle.
References
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