Functions and the Casio Calculator fog(x)

When finding fog(x) the CAS calculator does a good job of simplifying algebraic steps, often to the point of making traditional questions trivial in the calculator section.

I'll start by defining a function f(x) =2x+1 and g(x)=x^2 and attempting to find fof(x), fog(x) and the inverse of (fog(x)).

To define a function f(x) go to the Main window and select

Interactive->Define

A window will appear

Enter the function name (eg. f)
Variable (eg. x)
Expression (eg. 2x+1)

The main window will reply:
Define f(x)=2(x)+1
done

Repeat:

Interactive->Define
Enter the function name (eg. g)
Variable (eg. x)
Expression (eg. x^2)

The main window will reply:
Define g(x)=x^2
done


To find fof(x)

In the main window
Action->Transformation->simplify
f(f(x)) (using the soft keyboard)
press exe

The main window should say
simplify(f(f(x))
4x+3



To find fog(x)

In the main window
transformation->simplify
f(g(x)) (using the soft keyboard)
press exe

The main window should say
simplify(f(g(x))
2x^2+1



To find inverse of fog(x)

In the main window
action->transformation->simplify
action->assistant->invert
action->advanced->solve
y=f(g(x)),x))) (using the soft keyboard= don't forget the "y=")
press exe

The main window should say
simplify(invert(solve(y=f(g(x)),x)))

Here is a link to other CAS calculator posts.

Inverse Functions and the Casio classpad 330

The 3CD course requires knowledge of domain, range, co-domain and inverse functions. The classpad can handle these in a number of ways.

The most obvious way is in graph mode (Menu-> graph tab). Set up a graph (say y=(x+1)/(x+2), and visually examine it to find the domain and range. To find the inverse, click on the graph and select Inverse (Analysis->Sketch->Inverse). The equation of the inverse can be found by selecting the inverse graph and examining the equation bar at the base of the screen. Be careful with this method, as the resultant inverse graph is not written in "y=" form.

The less obvious way to do it is in the main window. I have not found an "inverse" function yet, but the following is a workaround to find the inverse.
Go
Action->Transformation->Simplify (to simplify the resultant equation)
Action->Assistant->Invert (to swap the x & y variables around)
Action->Advanced->Solve (makes x the subject of the equation)
Enter the function
Press ",x)))" using the soft keyboard (to make x the subject of the new equation)

It would look something like this when finished:

simplify(invert(solve(y=((x+2)/3,x)))

In a way I prefer the main window method as it mirrors the algebraic method. I think students need to really understand the parts of an equation to effectively find the domain and range. I explicitly draw students attention to critical information such as the inability of the function to equal zero or where the function is undefined

a) Look for possible values of x where y=1/0 will occur (eg. {x≠-1} for y=1/(x+1) ).
b) If it is not possible for the numerator to be zero (eg. {y≠0} for y=2/(x+1))

If the range is not obvious it is often easier to examine the domain of the inverse of the function.

Here is a link to other CAS calculator posts.

Purplemath has a good explanation of inverse functions.

Composite Area problems

With my year 10 "literacy focus" mathematics class we have been looking at the language of measurement, specifically area and perimeter. The idea has been to get students to clearly understand the importance of units and how to interpret what questions are asking.

When thinking about perimeter we are only thinking about the boundary outside a shape. We then looked at some real world shapes and measured their boundaries, followed by drawing some scale diagrams of shapes and measuring their boundaries.

We then tried to describe how much space was in the shapes. I tried to drive them to describing dimensions, but some students had enough prior knowledge to say calculate the answer by multiplying lengths.

The main issues came as we arrived at composite shapes where composite shapes had to be split into basic geometric shapes. Deriving missing measurements really brought home how much trouble low literacy students can have with basic mathematical concepts such as subtraction. Assuming that a student can see how to find missing sides is in many cases overestimating their ability.

Even at year 10, the majority of low literacy students fail to see f- c = a whereas they are more likely to be able to see a+ c = f.

Because of this to use a scale drawing to assist these students see subtraction in action requires some thought. If a student drew the above diagram with the following measurements they would
not use subtraction to find the missing side on the top rectangle. They would count the squares (if on grid paper) or measure the vertical gap and put the measurement of one on the page.

To encourage students to use subtraction I needed to encourage students to first look at the diagram and do a number of examples with them without using scale diagrams, explicitly doing subtraction sums. We checked our examples with scale diagrams, rather than finding the solution using scale diagrams.

Though a subtle difference, this was far more successful.






Another successful strategy used during these lessons was using formal layout during the early stages with simple examples. By doing this, students were able to see the connection between diagrams, algebraic substitution and the usage of formulae.

For instance:

















By learning this and ensuring each example was completed thus, when triangles and circles were introduced it was a trivial case of changing the formula and adding a line to the bottom

Area(Shape) = Area(S1) + Area(S2)

It was interesting to note that students at this stage had now forgotten that perimeter was the outer boundary and were including the S1 - S2 boundary in their perimeter calculations. It had to be explicitly explained that

Perimeter(Shape) != Perimeter(S1) + Perimeter(S2)

and that the intersecting boundary needed to be subtracted. For me, this is learning real mathematical literacy. Students are becoming able to exactly describe their intent on the path to a solution.

Issues with national curriculum

Today at a PD of five secondary schools and their mathematics teachers, we had a quick look at the national curriculum. As an upper school teacher, the demands of teaching upper school are significantly reduced under national curriculum with many upper school courses being pushed back into middle school and a lot of middle school algebra pushed into primary school. I don't necessarily think this is a bad thing.

Strengths that were raised by presenters were that it was put together by experts, that the course was being simplified (would contain less material with more depth), that when questioned by parents for course suitability teachers could point to the syllabus (reducing uncertainty) and that it assisted in course transferability (eg. between states).

The first issue identified by the audience was that it was a one size fits all approach. This means that many students will fail a year and then be unable to do the work in following years leading to students unable to achieve anything higher than a 'D' causing reduced motivation and higher instances of behavioural issues (for this reason alone I will re-iterate that anything other than normalised grades in classes is a poor solution).

The second issue was that for at least 5 years students will not have the capacity to complete middle and upper school mathematics as there are a considerable number of missing attributes in our current curriculum. Students taught under the current system will not be able to effectively participate under the new system without extensive remediation especially in operations and algebra. Given that this remediation needs to occur during an 'increasingly packed' lower school curriculum this is unlikely to occur.

The third issue relates to WA primary extending to yr 7 (resulting in a lack of specialist mathematics teachers in year 7) and primary schools being ill equipped to teach pre-algebra and algebra. Given the number of students that currently enter yr 8 'algebra ready' I tend to concur that this is a problem that could be solved by national curriculum (although nobody is saying how this will occur). I have no idea how long it will take for texts to be prepared and primary teachers upskilled to be able to present the material, but it will be longer than the current implementation date of 2011. No allowance for upskilling has been allocated to schools in low performing NAPLAN states WA, QLD, TAS and NT where the current curriculum is less rigorous due to population and historical factors.

The fourth issue relates to endpoints mapped in the current NCOS of study for year 12. Under the current plan there will be little requirement for 1B-2C as students will theoretically be well past the 2C benchmark if they successfully complete the yr 10 national curriculum. This caused some laughter and raised the more important point that we really need a range of courses 8-10 (focus, intermediate, advanced) to cater to a range of student abilities and to stream courses into NCOS subjects.

The fifth issue related to students in low SEI areas, where developmental lag is a real factor. The new curriculum has the potential to completely destroy students chances of catching up over the schooling years as students with a poor starting point are more likely to fall further and further behind as each year progresses. Furthermore, there is no allowance for students in current cohorts that are six months behind due to starting age differences between the states.

The sixth issue is that population size has to be a factor in determining the best course for a state. It will be harder for smaller states to generate the critical mass for harder courses, as the geographical aggregation of higher socioeconomic students is going to be attained in fewer areas. Running courses for 2-3 students is not going to be viable for many schools (especially with the attention on student/staff ratios) although not running these courses has catastrophic effects on staff retention (the best teachers will not go to schools without these courses running), student attraction (students that may have the potential (eg your top 10-15% will go elsewhere) and school morale.

One way to alleviate these issues raised by the group was to start holding students back if they could not meet the standard (eg pass the course with a fair chance of success in following years). This was dismissed as an unlikely solution by presenters although is a common solution in upper school courses.

It was not known by presenters whether accreditation to teach subject areas was being discussed (although that inference that this is a current agenda could be drawn from this media release by Julia Gillard yesterday). It's not a difficult prediction to make that implementation issues will be ignored, blame laid at teachers feet when the implementation fails in WA, QLD, TAS, NT, then an 'accreditation programme' instituted to identify capable teachers to deflect from the real issues listed above and the government policies that created the situation in the first place.

It was put by presenters that teachers had discussed all of this before at the start of (unit curriculum, OBE, 'insert other fad here') and we needed to just roll with the punches and get on with it as we always do. I think this is my main gripe about Julia Gillard, her inability to accept that this is the reality and that change is driven by government - not schools and that poor performance should be laid squarely by policy makers and change agents - not teachers. Furthermore, ill conceived ideas and implementation causes much angst amongst the teacher population and further resistance to change.

I don't think it is that the issues can't be overcome and that national curriculum will ultimately fail but a rushed implementation to political (4 year cycles) rather than educational (12 year cycles) is not appropriate. I still can't understand why this could not have started with a limited rollout and then moved across the country over the following decade using a staged approach. Given the rush for implementation and the suck it and see approach "the acceptance of ongoing failure before we find success", I think that this has the potential to cause a lot of heartache in the short to medium term.

I really hope those with the experience (and will) to guide us through this stand up and be counted. It's not only the students that will suffer in the long term.