## Tuesday, May 8, 2018

### Geometry: Teaching Composite Figures Vol and SA

Today was a good lesson in Geometry, so I thought I would share.  We are nearing the end of our surface area and volume unit.  Last week we did the project so they had the hands on aspect of learning the formulas.  They will get a formula sheet on the quiz.

Today's lesson was on composite figures and bringing them all together.  I thought I packed too much into the lesson but the timing was perfect which always makes me happy.

I started off with 2 lesson openers.  They both involving asking the students to make a prediction first.  They are so uncomfortable with this and start digging deeper and asking questions.  Just write a number down.  I did more 3Acts last year in Algebra 1, but haven't done them really in Geometry.

We started with this from Dane Ehlert and which is bigger?  I asked them to write down shape A or B and then I asked what I could give them that might make it easier.  They said the area.  I said I wouldn't just give them the area but I would give it to them on the grid.  I was surprised how quickly they jumped to their calculators and formulas.  I didn't anticipate that.  I just counted the boxes.  It made for good conversation.

The second one was a 3Act from Kyle Pearce at www.tapintoteenminds.com He does a great job on his website explaining the lesson, providing resources including worksheets and videos.  I showed the picture of a house with a lawn and asked them what they noticed and what they wondered?  We eventually got to the lawn but it is a very geometric house.  We could have asked more about the house.  We finally came up with how long will it take to mow the lawn.  I asked them to write down a prediction, but again they wanted more first.  Then, in Act 2, I asked what more I could give them so they could calculate it and they asked for area.  I told them I wouldn't give them area directly, but what could I give them....dimensions.  They asked about the lawnmower, if it was a push (gasp, it was), how wide it was, and they wanted a rate.

I showed them a 3D diagram of the lawn and explained it was similar to our project last week when we had a challenging time drawing that sort of flattened back drawing.

I handed out the worksheet and asked them to find the perimeter and area of the lawn.  Then, I showed the video of the actual lawn mower so we could get the rate.

Act3 was showing the real answer.  I won't give it away, but our number was a little lower than the actual time and we talked about possible discrepancies.

Finally, we moved onto board problems.  I overheard a students say, "I love board problems; different every time but still fun."  This made my day :)

Usually I make these board problem oral problems in geometry, but the shapes were too complicated.  I had three different shapes and asked for Volume and Surface area of each, in groups of 3 with only one marker at a time, but everyone calculating on their calculators.  It took a bit.  They would check in with me and it felt like the Price is Right again as I told them their answer was too high or too low.  But, they stuck with it.  There were so many great conversations - lots of "I think we went wrong here." "We need to subtract this circle" or "we need to add this cylinder's lateral area."

Here is the powerpoint.
Here are the board problems.

Thanks for reading. Happy Teacher Appreciation Week!