Friday 4 December 2015

MPM2D - Day 60: Completing the Square, Day 1

We started today by looking for patterns in perfect square trinomials.

They noticed the pattern which we consolidated:

Then we looked at it another way. In groups of four, they each answered one of these questions and then wrote the sum of the four answers in the middle box. This allows me to quickly see if they are correct and, if they are not, they have to work together to figure out which question(s) are wrong.

We talked about how we can find the vertex of a parabola. Factor the quadratic, take the average of the zeros, then substitute that value back in the equation. But what if you can't factor the quadratic? One student said he could always find the zeros... "Desmos!", he said :) Then the algebra tiles came out and we starting completing the square.

The idea of making a square is not difficult when they work with the tiles. We kept the 7 unit tiles off to the side and then added one positive unit tile to fill in the square. This meant that we also needed to add one negative unit tile to ensure that we weren't changing the value of expression. Writing the equation in vertex form was quite straightforward, as was stating the vertex.

I gave them the steps - this may be useful for those students who were away today.

Then we practiced some more.

It was time to start to move toward an algebraic solution so we started by noticing what is happening with the numbers, and then repeated one of the previous examples without tiles.

We did a few more examples.

Along the way we talked about why we needed to move away from the tiles. What if the number of x-tiles was not even? But we did a simple case together with tiles - not the actual tiles though, as I do not want them split in half! 

Today's homework was to go back over any old homework that they had either not completed or done incorrectly. Next class we will look at cases where the a-value is not 1.

1 comment:


    Best thing I've ever seen on quadratics. I show the second group of videos on completing the square to all my intermediate algebra classes before teaching the standard approach to completing the square and then let the students choose which approach they prefer. Most find Tanton's method more sensible and useful, though of course they both are mathematically sound.