Engaging students: Finding the area of a right triangle

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission again comes from my former student Jessica Bonney. Her topic, from Geometry: finding the area of a right triangle.

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What interesting word problems using this topic can your students do now?


Since students have learned the area of a rectangle, we can use this previously learned knowledge to help students better understand the area of a right triangle. To start off the class you could say that a farmer needs our help developing his pasture into two hay meadows, one for warm-season grass and the other for cool-season grass. The large, rectangular pasture measures 250 yards wide and 600 yards long. Hancock Seed Company sells bahia grass(warm-season grass) seed for $140 per 50-lb bag per acre and ryegrass (cool-season grass) seed for $25 per 50-lb bag per acre. Have the students initially calculate the area of the pasture, then the area of the area of each triangle. From there the students can calculate how many acres are in each triangular section of pasture to determine how many pounds of seed the farmer will need. This activity allows the students to investigate and see the relationship between the area of a triangle compared to the area of a rectangle in a real world setting.

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How can technology (YouTube, Khan Academy [khanacademy.org], Vi Hart, Geometers Sketchpad, graphing calculators, etc.) be used to effectively engage students with this topic?


Khan Academy has a great tool for showing students the area of a right triangle (https://www.khanacademy.org/math/geometry-home/geometry-area-perimeter/geometry-area-triangle/a/area-of-triangle). This tool allows students to see how the area of a triangle correlates to the area of a rectangle. By clicking on the dot and dragging it, the user can see why the formula for the area of a triangle works. Students should have previously learned that the area of a rectangle is the base multiplied by the height (A=bh). This interactive tool shows students that the area of a triangle is one half the area of a rectangle (A= ½ bh). Through further interactions on the website the students then can transform the triangles to rectangles and solve to find the area of the triangle. For further explanation of the formula, Khan Academy has a video demonstrating and proving the area of a triangle using methods from Euclid’s Elements, but in a much simpler form so that students will be able to follow along.



Khan Academy: https://www.khanacademy.org/math/geometry-home/geometry-area-perimeter/geometry-area-triangle/a/area-of-triangle


Trigonometry for Physics: http://www.lshsstem.com/uploads/3/9/1/4/39145399/phy_1_trig_for_physics.pdf


Khan Academy: https://www.khanacademy.org/math/trigonometry/trigonometry-right-triangles


Radford University: http://www.radford.edu/rumath-smpdc/Units/src/Poles_Sports.pdf


Hancock Seed Company (Bahia Grass Seed): https://hancockseed.com/hancocks-pensacola-bahia-grass-seed-50-lb-bag-4.html


Hancock Seed Company (Ryegrass Seed): https://hancockseed.com/hancocks-ryegrass-seed-50-lb-bag-14.html



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