Introducing Trig through Slope

Here is our lesson today to introduce trigonometry for the first time. We had spent a few days with solving problems with similar triangles. We are spiralling and have done  lots of work recently using slope and the distance formula to classify triangles. I wanted to capitalize on that familiarity with slope to introduce the tangent ratio for the first time.

We started with this….again

Most students like last time chose A and their reason was it was less steep. So I asked “How much less?” “How do we measure that?”……SLOPE was the response and they calculated the slopes to verify.

Next I had them do this…
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I stressed supreme accuracy and added “Try to create a size of triangle you think no one else will make”……I had them measure their rise and run and enter them in this table on the board.


I also kept a running table in Desmos…


As more students added their triangles I could hear them say, “I bet all the slopes should be the same” , “They’re all similar triangles” We took a moment to discuss similarities and make it clear we all have similar triangles and that the ratio between the rise and the run should all be the same. We also discussed why some of our triangles did not have a slope of 1.7. I had them repeat the process with an angle of 45 degrees.


I said out loud that MY slope ratio was 1….and I could see all their heads bobbing up and down….”Yep, we got 1 too”.


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I asked them again to create an angle/triangle (Had them keep the same orientation of the triangle as I did in my diagram) that no one else would.

Measure the rise and the run, then calculate your slope. Keep your triangle and slope hidden, especially from ME.

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Keeping their angles and ratios hidden from me I said…”When I point to you tell me your angle….and I’ll magically tell you your slope” Cue the Oooohs and aaaahs.

I played up the magic bit. I held my calculator up to shield the screen from them.

I pointed at one student they told me “34 degrees”. I punched on my calculator mysteriously and said…”0.67.” The student yelled out….”Hey that’s right”. I went around the room pointing at students and telling them their slopes (ratios). I could see it on their faces, they wanted to know how I was doing this……Boom Let’s talk about Trigonometry.

So I said:

“In math we have these things called functions….they’re like black boxes that take an input and do some number crunching and spit out an output. One function you have used already is the square root function. You give the function 9 and it spits out 3. We math people use a symbol for this function so we all know what is going on. There is another function that will calculate the slope of a right triangle if you give it the angle. So we could write something like this “(I used one of the students angles).


“This is what I was doing when you gave me your angles….I was using the function to calculate your ratio between rise and run. But we don’t usually use the term slope when we talk about right triangles. We use fancy words.” I had them draw a right triangle in their notes and we labeled it with Hypotenuse, opposite and adjacent. Screen Shot 2015-10-08 at 5.07.34 PM

“Instead of using a slope function…..we use the word TANGENT. And instead of using the word rise we use the word OPPOSITE and instead of run we use ADJACENT. So we can write this tangent function equal to the rise/run = opp/adj.”

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“And we math people don’t like to write too much so we really use this version.”

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Then we practiced using the tangent button on our calculators. They pretended to be the magicians and checked each others ratios. We practiced using the inverse tangent button to find angles.

Once we were comfortable we moved into writing the ratio and finding the angle out. We also used this example to write the tangent ratio of the other angle.Screen Shot 2015-10-08 at 2.21.05 PM

and then one more for lengths:

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Since we are spiralling I gave them the homework set (Mary Bourassa Style) to work on….here.

Tomorrow I’ll introduce the Sine and Cosine function.

Using slope here to introduce trig allows us to take something familiar and make something new. Students could see the progression happen and not have trig just thrown at them.

Would to love to hear your thoughts on this. How do you introduce trig?


R2D2 – Pear Deck/Desmos Mash Up!

School is just right around the corner for us up here in Ontario and I can’t stop thinking about that first day. As for my grade 9 applied class’ first day I have ran the R2D2 problem in the past with great success.
Now, over the summer I’ve seen great improvements in Pear Deck and wanted to get into it! Also Desmos has been busy and released Activity Builder!! So let’s mash these two apps up with some R2D2!!

So here is the R2D2 problem presented with Pear Deck and an extensions with Desmos….

Act 1: The video

and this is what Pear Deck will show after you insert the video… how the video will be displayed on the projector and not on each individual device!!!


I like using Pear Deck here for asking for wonderings and notices because it allows students who normally won’t shout out answers to have a voice in the room. Students get to input their responses and the teacher can show them on the projector.

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For generating estimates I absolutely love how they put our Too high and Too low guess on a number line… gives us the visual of where our actual estimates will lie.


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Act 2: Gathering the Info

In the new version here I get students to draw their estimates of the dimensions of both the board and the post it note…..this pushes them into drawing diagrams.



Revealing the dimensions….


Students are ready to solve….



Act 3: Revealing The answer

The Extension: How many rectangles can we make that have an area of 609 post it notes?
To extend I want students draw out different rectangles and label their dimensions! They can use Pear Deck’s white board!


But then they can enter them into Desmos through a pre-made activity I created in Activity Builder. (the Pear Deck file links to the Desmos activity).

For each rectangle the student can come up with they find the perimeter and plot the length vs. perimeter in the Desmos graph. The teacher on the projector can use the Overlay function and show all the different rectangles students are coming up with…essentially showing the pattern that emerges! Using the pattern students can read off the minimum perimeter!


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If you have a Pear Deck account Grab and download the file below!

Link to the Desmos Activity

Final Assignment – Estimation Challenge

For our final activity I started the off with this……

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we filled in too high, too low, and best guesses! Then we checked the answer…..

Completing this challenge got the students pumped and hooked into doing some math on our very last days of class (especially with some students exempted from the final exam). Our final assignment is to …

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We got out the iPads and I let the kids work….. here is what a few came up with:

A lot of kids did water filling or post it note covering estimates. Some kids ended up making an all-out 3 Act math problem.


How many caps will fill the marker?

Estimate & Answer



How many cups to fill the shape?
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A 3- act task in Explain Everything:

How many post-its will cover this triangular wall:

Act 1: She put a photo and a small video in Explain Everything to start us off.
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Act 2: She provided us with a little more info after we made some guesses.
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Act 3: Made a time lapse video and provided a screen shot with the answer

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Grab her Explain Everything File here




How many stickies to fill the door window?

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And hit us up with a time lapse video for the answer:




How many water bottles will fill the hexagonal prism?


and the answer


Watch the water fill up by grabbing her Explain Everything File

A fun last few days….and I’ve got some new estimates for class next year.

Is Lego Gender Biased?

Here was how our conversation in math class (MFM1P) went…..How many pieces make up this Star wars Lego ship? Screen Shot 2015-02-23 at 3.28.54 PMWe started with that picture and had a great conversation around Lego.

Then I showed this one.

Does the pool/hot tub have more pieces/less pieces/ or the same? This turned into “boy” Lego vs. “girl” Lego. My personal opinion is its all great…. My 3 daughters are just as excited to play with Yoda as they are with Disney princesses. Girls in the class agreed that they didn’t need their own line of lego!!!

I moved our conversation a little forward with asking Which costs more? And which should cost more?

Screen Shot 2015-02-24 at 5.46.05 AMAnswers: Continue reading