Tag Archives: parallelogram

Visuals for Area Formulas

March came and went in a blur!  And now it is the last week of April already. During the month of April, the 7th graders were studying the area formulas for rectangles, parallelograms triangles, trapezoids, and circles.  Instead of just giving students a formula, I wanted them to understand where the formula came from.

We started with the area of a rectangle and parallelogram.  Since I was out that day, I changed this activity to a step-by-step instruction from illuminations.org so students could work independently to discover the formula for a parallelogram.  When I got back the next day, we reviewed the activity and I put a large visual on one of my bulletin boards that I made from poster board.

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Then we found the area of a triangle and trapezoid by cutting the parallelogram in half.

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Finally, we cut a circle into equal-sized sectors and arranged them to resemble a parallelogram.   Since the circle has an area closely related to the parallelogram, we used the formula for the area of a parallelogram to find the area of a circle.

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Whenever we did an activity involving the formulas and students asked me what a specific formula was, I pointed to the bulletin board and asked them what they thought it would be.  We continually referred back to the visuals and talked about how the formulas were derived.  The visuals will stay up through our unit on volume.  Hopefully, students will understand the formulas rather than just memorize them.

 

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