Logarithms

In last week’s post I talked about the work that we had completed on indices and how we were using this to launch logarithms and exponentials this week. The benefits of this approach were shown up during one of the indices lessons when one of the students was tackling the following question (taken from Stuart Price’s Problem Book, @sxpmaths):

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He asked if there was an easier way to tackle problems like this, suggesting that if the numbers were much bigger it would make the problem more difficult. This was a perfect opening for introducing logarithms, which we did with a series of similar questions.

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When planning this lesson in discussion with Will, we felt that this approach really emphasised the link between indices and logarithms, something that we both felt had been missed by some students in previous years. We felt that the best way to do this was by talking about functions and their inverses. Yes, inverse functions is strictly a second year topic and they wouldn’t need it for their exams in the first year, but it is the connection that has been lost in the past and the reason students struggle with the topic.

In order to build these links we created a Geogebra file that allowed us to turn on an off a series of functions and their inverses. We had it set up to display a couple of linear graphs, a quadratic and then an exponential – the goal being to draw out that the inverses were a reflection in the line y=x. This had students already trying to tell us what shape the inverse of an exponential should be, before we even introduced what the function truly was. I’ve used a similar approach before, but not incorporated the graphs – so the connections were already stronger than they had been for students in the past.

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The next part of the lesson formalised the notation of logarithms, after which we went back to these questions and rewrote them as logarithms, solving the later ones using our new calculators as we went.

The next lesson began with a recap starter, but this time we took the students a bit further…

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They were all able to calculate the answers on their calculators, but actually explaining why was missing, and there was no real notation or workings out (yet). So when we went back through these questions we modeled taking logs of both sides of the equation, or using both sides as powers with an appropriate base. Then we could discuss that as the two functions that we’d composed were inverses that their effects cancel. All designed to reinforce the links between logarithms and exponentials as well as to lay the groundwork for exponential / logarithmic equations.

In the past we’d found that students can be quite unreliable at remembering the laws of logs, despite the connection to the rules of indices – perhaps down to the split in topics between C1 and C2. On our scheme of work this split is non-existent as we’ve run the topics together. We also decided that to further emphasise the link that we would start with the indices rules and from them actually derive the laws of logs – this might go over the heads of some of the students, but they’d have it to look back and reflect on, plus we knew that there would be a good proportion of our group that would embrace knowing why this rule exists. After doing the product law we let the students try to work out the quotient law, and even to have a go at creating the derivation on their own. This also built on our previous work on proof and on how to construct a solid mathematical argument.

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After we’d derived all the rules, the next step would be usually be to work through a series of examples, with students copying them down. As they’d already done a lot of writing I gave them the complete examples and we went through them with the students annotating why things were happening, and what rule was being used to do these things.

When we introduced ex we got the students to plot graphs in a template that we had created in Geogebra – the idea being that after they had plotted 2x and 3x and examined their gradients at each of the points we had given them that they would see that at each point,  ex has the same gradient as y-value. The group were fairly pleased with their discovery, and it allowed us to give them the reason why e is so special that it has been given its own letter. We did have one query though: “how did they calculate the value of e, so that it is the value that will them give it its own gradient?” – this came from a further mathematician, and that question became his homework.

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Much of the rest of the topic was fairly standard – log equations, hidden quadratics involving exponential equations, but with the addition of ex and ln( ) ≡ loge( ) for the new spec, however we did make one tweak to what will has been taught in the past. We felt that students could not pick up how to add logs to a term that does not have them in so that they can then combine them using the laws. Even just these 4 questions that we started together were enough to give them something to work from in the future.

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Overall we were very pleased with how the teaching of logarithms progressed over the week. In order to assess what we had covered we asked students to complete one of the Integral online assessments. Hopefully as this comes back we will see that students have a greater understanding than we have seen in previous years.

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An update from the start of term

In the recent posts we have been focusing on the statistics elements of the new course. It is now time for an update on the general running of the course and the pure elements.

Firstly some background information on the new A-level group. In previous years we have offered the maths A-level in two different option blocks meaning that we have had two groups of around 10 – 12 students. With drop off as students have dropped from four to three subjects at the end of year 12 this has meant groups of 5 – 8 in year 13. This has now been considered uneconomical so we have been reduced to one option block, as it was thought impossible to combine the two groups at the end of year 12. Of course having had this decision imposed on us, we then had a greater take up of maths meaning a class of 26. The balance of this class is also unusual due to a foreign exchange programme meaning that we have a large number of foreign students joining us for the year (two Swedes, two Mexicans, one American and one Romanian). These students will leave at the end of year 12 leaving a much more manageable year 13 group.

In practical terms the sharing of the content evenly has gone extremely well, with us being able to have frequent conversations about the direction of the lessons, despite the added pressure on my time due to being head of department this year.  This has been even better than expected, as having the dialogue has meant (certainly for me and I hope for Will), that the actual planning of the lesson has been easier as I already know what I want to achieve. We have been careful to make sure that both of us have taught both pure content and statistics content to avoid being pigeon-holed as the ‘pure’ teacher and the ‘stats’ teacher.

Another positive has been the use of technology in lessons. In the first three weeks of term I have already booked and used a computer room more than I had in the previous two years. All of the students have now got their new calculators and we are settling into using them – I even treated myself to a new one, replacing the one I had used since I did my A-levels 16 years ago.

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Our first lesson looked at extending GCSE proof. We felt that it was really important to introduce proof as one of our key themes as early as possible. We asked students to choose from a variety of ideas, both algebraic and geometrical, to see what they could come up with. We then discussed what a proof should look like and worked on developing the skills required to build a mathematical argument. This is something that we will be returning to regularly, making sure that students are getting more accomplished.

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Our first major topic was indices and surds. As this is largely revision of GCSE topics we decided to approach it by setting pre-learning tasks and then developing the knowledge already in place. The tasks we set were the ‘walkthroughs’ from Integral Maths. These walk students through the required knowledge of the topic, introducing ideas and allowing experimentation in an interactive way. Students are allowed as many attempts as required without it being recorded and reported to teachers.

For the indices section of the week we used the online textbook ‘Problem Book for A-level Maths’ being developed by Stuart Price (@sxpmaths on Twitter). We really like the way that this has sections for students who are at different stages of development, starting with technique for those who need more work on the basics and progressing through problem solving to puzzles & challenge. Our grade 9 students had great fun going straight onto the challenge problems, while others were absorbed by the technique section. They were also able to move backwards and forwards if required. There is also a final section for each topic which covers exam style question practice, although we did not get to this – something to use in the future.

For the surds section we used an adaptation of an activity from Integral Maths (pictured below) where students discussed how surds are simplified. We deliberately left some expressions that had not been fully simplified and asked students to present their findings to each other. Additional questions for this lesson were taken from Dr Frost Maths (@DrFrostMaths).

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We have been really enjoying using materials from a variety of sources and with different styles. Students seem really enthused and have been seeking us out for extra support when needed. Our next topic is exponentials and logarithms. The logic behind this is that we wanted students to experience something totally new early in the course. We also felt that they fitted very well together, essentially being two different ways of looking at the same topic. I always felt that the two ends were rather artificially kept apart by the arbitrary barrier between C1 and C2, now I have the opportunity to try and teach them together.

Hopefully I will have time for an update next week!