I will first model how to measure the area of a triangle using a ruler. Here is an opportunity for students to get more practice using an appropriate tool (MP5); it is also an opportunity for me to practice patience. My more active students will think the rulers are drum sticks or swords! Measuring the base and height of a triangle using a ruler requires students to attend to precision (MP6). Students will not only have to make decisions about how precise to measure each dimension, but students must be aware that the base and the height are perpendicular to each other. I will NOT ask students to use protractors to make sure they have a 90 degree angle, but I’ll expect them to estimate well. When the height of a triangle is not one of its sides, I’ll expect to see dotted lines denoting the height. I would like to have some good examples to display so I’ll ask my students to write neatly. This is a do as I say not as I do moment, since my handwriting can sometimes be less than ideal! For each shape that we measure, I’ll set a time limit of a few minutes. To hone in on the idea of surface area being a measurement of unit squares, for each shape I will ask students to tell me how many squares of a relevant unit will cover the face of the shape. This may seem obvious, the answer is the surface area, but I like to make sure my students understand what the unit of measurement is.
I allowed students to decide whether to measure in the metric system or the customary system. Not surprisingly, most students choose the metric system. When I asked why, they said it was easier for them to work with decimals. I can't say I disagree with that choice. I did encourage several students to measure at least one shape using the inches. I thought they could use the practice working with fractions and I wanted a variety of labels for measurements.
Students will be asked to find the surface area of a square pyramid using its net and a ruler. If time permits, we will discuss solutions to the exit ticket.