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**Have you got a Super Brain?**

Adapting and exploring maths challenge problems is an excellent way of finding ideas for IB maths explorations and extended essays. This problem is taken from the book: The first 25 years of the Superbrain challenges. I’m going to see how many different ways I can solve it.

The problem is to find all the integer solutions to the equation above. Finding only integer solutions is a fundamental part of number theory – a branch of mathematics that only deals with integers.

**Method number 1: Brute force**

This is a problem that computers can make short work of. Above I wrote a very simple Python program which checked all values of x and y between -99 and 99. This returned the only solution pairs as:

Clearly we have not proved these are the only solutions – but even by modifying the code to check more numbers, no more pairs were found.

**Method number 2: Solving a linear equation**

We can notice that the equation is linear in terms of y, and so rearrange to make y the subject.

We can then use either polynomial long division or the method of partial fractions to rewrite this. I’ll use partial fractions. The general form for this fraction can be written as follows:

Next I multiply by the denominator and the compare coefficients of terms.

This therefore gives:

I can now see that there will only be an integer solution for y when the denominator of the fraction is a factor of 6. This then gives (ignoring non integer solutions):

I can then substitute these back to find my y values, which give me the same 4 coordinate pairs as before:

**Method number 3: Solving a quadratic equation**

I start by making a quadratic in x:

I can then use the quadratic formula to find solutions:

Which I can simplify to give:

Next I can note that x will only be an integer solution if the expression inside the square root is a square number. Therefore I have:

Next I can solve a new quadratic as follows:

As before I notice that the expression inside my square root must be a square number. Now I can see that I need to find m and n such that I have 2 square numbers with a difference of 24. I can look at the first 13 square numbers to see that from the 12th and 13th square numbers onwards there will also be a difference of more than 24. Checking this list I can find that m = 1 and m = 5 will satisfy this equation.

This then gives:

which when I solve for integer solutions and then sub back into find x gives the same four solutions:

**Method number 4: Graphical understanding**

Without rearranging I could imagine this as a 3D problem by plotting the 2 equations:

This gives the following graph:

We can see that the plane intersects the curve in infinite places. I’ve marked A, B on the graph to illustrate 2 of the coordinate pairs which we have found. This is a nice visualization but doesn’t help find our coordinates, so lets switch to 2D.

In 2D we can use our rearranged equation:

This gives the following graph:

Here I have marked on the solution pairs that we found. The oblique asymptote (red) is y = 2x-1 because as x gets large the fraction gets very small and so the graph gets closer and closer to y = 2x -1.

All points on this curve are solutions to the equation – but we can see that the only integer solution pairs will be when x is small. When x is a large integer then the curve will be close to the asymptote and hence will return a number slightly bigger than an integer.

So, using this approach we would check all possible integer solutions when x is small, and again should be able to arrive at our coordinate pairs.

So, 4 different approaches that would be able to solve this problem. Can you find any others?

**You can download all 17 of the Paper 3 questions for free here:** [**PDF**].

**The full typed mark scheme is available to download at the bottom of the page.**

**Seventeen IB Higher Level Paper 3 Practice Questions**

With the new syllabus just started for IB Mathematics we currently don’t have many practice papers to properly prepare for the Paper 3 Higher Level exam. As a result I’ve put together 17 full investigation questions – each one designed to last around 1 hour, and totaling around 40 pages of questions and **600 marks** worth of content. This has been specifically written for the Analysis and Approaches syllabus – though some parts would also be suitable for Applications.

Below I have split the questions into individual pdfs, with more detail about each one. For each investigation question I have combined several areas of the syllabus in order to create some level of discovery – and in many cases I have introduced some new mathematics (as will be the case on the real Paper 3).

**Topics explored:**

**Paper 1: Rotating curves: **[Individual question download** here**. Mark-scheme download** here.**]

Students explore the use of parametric and Cartesian equations to rotate a curve around the origin. You can see a tutorial video on this above. The mathematics used here is trigonometry (identities and triangles), functions and transformations.

**Paper 12: Circumscribed and inscribed polygons **[Individual question download **here**].

Students explore different methods for achieving an upper and lower bound for pi using circumscribed and inscribed polygons. You can see a video solution to this investigation above. The mathematics used here is trigonometry and calculus (differentiation and L’Hopital’s rule).

**Paper 2: Who killed Mr. Potato? **[Individual question download **here****.**]

Students explore Newton’s Law of Cooling to predict when a potato was removed from an oven. The mathematics used here is logs laws, linear regression and solving differential equations.

**Paper 3: Graphically understanding complex roots **[Individual question download **here.**]

Students explore graphical methods for finding complex roots of quadratics and cubics. The mathematics used here is complex numbers (finding roots), the sum and product of roots, factor and remainder theorems, equations of tangents.

**Paper 4: Avoiding a magical barrier **[Individual question download **here**.]

Students explore a scenario that requires them to solve increasingly difficult optimization problems to find the best way of avoiding a barrier. The mathematics used here is creating equations, optimization and probability.

**Paper 5 : Circle packing density** [Individual question download **here**.]

** **Students explore different methods of filling a space with circles to find different circle packing densities. The mathematics used here is trigonometry and using equations of tangents to find intersection points.

**Paper 6: A sliding ladder investigation **[Individual question download **here**.]

Students find the general equation of the midpoint of a slipping ladder and calculate the length of the astroid formed. The mathematics used here is trigonometry and differentiation (including implicit differentiation). Students are introduced to the ideas of parametric equations.

Paper** 7: Exploring the Si(x) function **[Individual question download **here**.]

** **Students explore methods for approximating non-integrable functions and conclude by approximating pi squared. The mathematics used here is Maclaurin series, integration, summation notation, sketching graphs.

**Paper 8: Volume optimization of a cuboid **[Individual question download **here.**]

** **Students start with a simple volume optimization problem but extend this to a general case of an m by n rectangular paper folded to make an open box. The mathematics used here is optimization, graph sketching, extended binomial series, limits to infinity.

**Paper 9: Exploring Riemann sums **[Individual question download **here**.]

Students explore the use of Riemann sums to find upper and lower bounds of functions – finding both an approximation for pi and also for ln(1.1). The mathematics used here is integration, logs, differentiation and functions

**Paper 10 : Optimisation of area **[Individual question download **here**.]

Students start with a simple optimisation problem for a farmer’s field then generalise to regular shapes. The mathematics used here is trigonometry and calculus (differentiation and L’Hopital’s rule)

**Paper 11: Quadruple Proof **[Individual question download **here.**]

Students explore 4 different ways of proving the same geometrical relationship. The mathematics used here is trigonometry (identities) and complex numbers.

**Paper 13: Using the binomial expansion for bounds of accuracy **[Individual question download **here**.]

Students explore methods of achieving lower and upper bounds for and non-calculator methods for calculating logs. The mathematics used here is the extended binomial expansion for fractional and negative powers and integration.

**Paper 14: Radioactive Decay **[Individual question download **here**.]

Students explore discrete decay models, using probability density functions to investigate the decay of Carbon-14 and then explore the use of Euler’s method to approximate more complex decay chains. The mathematics used here is integration, probability density functions and Euler’s method of approximation

** Paper 15: Probability generating functions [**Individual question download **here**.**]**

Students explore the use of probability generating functions to find probabilities, expected values and variance for the binomial distribution and Poisson distribution for predicting the eruption of a volcano.

**Paper 16: Finding the Steiner inellipse using complex numbers [**Individual question download **here]**

Students use a beautiful relationship between complex numbers and an ellipse tangent to the midpoints of a triangle. This relationship allows you to find the equation of an ellipse from coordinate points of a triangle.

**Paper 17: Elliptical curves** [Individual question download **here**]

Students explore a method for adding points on an elliptical curve. This has links with elliptical curve cryptography.

**Mark-scheme download**

[If you don’t have a PayPal account you can just click on the relevant credit card icon]

IB HL Paper 3 Practice Questions and markscheme.

100 pages of preparatory questions with answers for the IB HL Analysis P3 exam. Please note this is not an automatic download and will be sent the same day.

$9.00

IB HL Paper 3 Practice Questions and markscheme AND Exploration Guide

All the Paper 3 questions and mark scheme AND the 63 page Exploration Guide. The Exploration Guide includes: Investigation essentials, Marking criteria guidance, 70 hand picked interesting topics, Useful websites for use in the exploration, A student checklist for top marks, Avoiding common student mistakes, A selection of detailed exploration ideas, Advice on using Geogebra, Desmos and Tracker. And more! Please note this is not an automatic download and will be sent the same day.

$14.00

**Complex Numbers as Matrices – Euler’s Identity**

Euler’s Identity below is regarded as one of the most beautiful equations in mathematics as it combines five of the most important constants in mathematics:

I’m going to explore whether we can still see this relationship hold when we represent complex numbers as matrices.

**Complex Numbers as Matrices**

First I’m I’m going to define the following equivalences between the imaginary unit and the real unit and matrices:

The equivalence for 1 as the identity matrix should make sense insofar as in real numbers, 1 is the multiplicative identity. This means that 1 multiplied by any real number gives that number. In matrices, a matrix multiplied by the identity matrix also remains unchanged. The equivalence for the imaginary unit is not as intuitive, but let’s just check that operations with complex numbers still work with this new representation.

In complex numbers we have the following fundamental definition:

Does this still work with our new matrix equivalences?

Yes, we can see that the square of the imaginary unit gives us the negative of the multiplicative identity as required.

More generally we can note that as an extension of our definitions above we have:

**Complex number ****multiplication**

Let’s now test whether complex multiplication still works with matrices. I’ll choose to multiply the following 2 complex numbers:

Now let’s see what happens when we do the equivalent matrix multiplication:

We can see we get the same result. We can obviously prove this equivalence more generally (and check that other properties still hold) but for the purposes of this post I want to check whether the equivalence to Euler’s Identity still holds with matrices.

**Euler’s Identity with matrices**

If we define the imaginary unit and the real unit as the matrices above then the question is whether Euler’s Identity still holds, i.e:

Next I can note that the Maclaurin expansion for e^(x) is:

Putting these ideas together I get:

This means that:

Next I can use the matrix multiplication to give the following:

Next, I look for a pattern in each of the matrix entries and see that:

Now, to begin with here I simply checked these on Wolfram Alpha – (these sums are closely related to the Macluarin series for cosine and sine).

Therefore we have:

So, this means I can write:

And so this finally gives:

Which is the result I wanted! Therefore we can see that Euler’s Identity still holds when we define complex numbers in terms of matrices. Complex numbers are an incredibly rich area to explore – and some of the most interesting aspects of complex numbers is there ability to “bridge” between different areas of mathematics.

For students taking their exams in 2021 there is a big change to the IB syllabus – there will now be 4 possible strands: IB HL Analysis and Approaches, IB SL Analysis and Approaches, IB HL Applications and Interpretations, IB SL Applications and Interpretations.

**IB Analysis and Approaches**

There is a significant cross-over between the current SL and HL courses and the new Analysis courses. The main differences are:

- The SL course will now be a complete sub-set of the HL course, and the HL exam will now include some of
*the same*questions as the SL exam. Previously whilst SL was almost a complete sub-set of the HL course, the questions on the HL paper were never the same as SL (and usually all significantly harder). - There are a few small additions to the HL Analysis syllabus compared to the old HL syllabus – such as binomials with fractional indices, partial fractions and regression. SL will be largely the same except that the unit on vectors has been taken out.
- The HL option unit has gone – and some of the old HL Calculus option has been added to the core syllabus (though only a relatively small proportion of it).
- HL students will instead do an investigation style Paper 3 – potentially with the use of technology. This will lead students through an investigation on any topic on the syllabus.
- The Exploration coursework will remain – however the guidance is now that it should be 12-20 pages (rather than 6-12 previously).

**What does this all mean?**

Until we start to see some past papers it’s difficult to be too confident on this – but based on the syllabus and specimen paper I would say that the two new courses remain pitched at the same level as for the old SL and HL courses. Therefore the Analysis and Approaches HL course is only suitable for the very best mathematicians who are looking to study either mathematics or a field with substantial mathematics in it (such as engineering, physics, computer science etc). These students would usually have an A* at IGCSE and have also studied Additional Mathematics prior to starting the course. The Analysis and Approaches SL course looks like it will still be a good quality mathematics course – and so will be aimed at students who need some mathematical skills for their university courses (such as biology, medicine or business). These students would usually have an A* – B at IGCSE.

**Resources for teachers and students**

This will be a work in progress – but to get started we have:

**General resources:**

1) A very useful condensed pdf of the Analysis and Approaches formula book for both SL and HL.

2) An excellent overview of the changes to the new syllabus – including more detailed information as to the syllabus changes, differences between the two courses and also what 10 of the leading universities have said with regards to course preferences.

3) University acceptance. Information collated by a group of IB teachers on university requirements as to which course they will require for different subjects (this may be not be up to date, so please check).

4) Christos Nikolaidis has put together a fantastic site which has full class notes on the entire Analysis syllabus, along with tests and exercises. This is all free – and a superb resource.

5) I’ve just put together thirteen full investigation questions – each one designed to last around 1 hour, and totaling around 30 pages and **450 marks** worth of content. There is also a fully typed up mark scheme. Together this is around 100 pages of content.

6) There’s a brand new question bank called IB Taskmaster. It has all original questions – which you can use to create practice tests on all topics. All free to use – currently over 600 questions and markschemes available.

**Specific resources for the new HL and SL syllabus content:**

**1. Linear correlation (previously only SL, now SL and HL)**

a) A worksheet (docx file) on using a GDC to calculate regression lines and r values.

**2. Equation of regression line of x on y. (SL and HL)**

**3. Sampling (SL and HL)**

**4. Simple deductive proof (SL and HL)**

a) A deductive proof worksheet (docx file) with some simple examples of deductive proof.

**5. Partial fractions. (HL)**

a) A Partial Fractions worksheet (docx file) with notes and some partial fraction questions.

**6. Binomial expansion with fractional and negative indices (HL)**

a) A binomial expansion worksheet (docx file) requiring the use of fractional and negative indices, as well as use of the Maclaurin expansion.

**7. More rational functions (HL)**

**8. Graphing [f(x)] ^{2}**

**(HL)**

**9. L’Hopital’s rule (Previously on the Calculus option now on HL)**

a) A Limits of functions worksheet (docx file) with some examples of simple limits and uses of L’Hopital’s rule. Markscheme here.

**10. Euler method for differential equations (Previously on the Calculus option now on HL)**

a) A worksheet (docx file) with some questions using Euler’s method to solve differential equations.

**11. Separating variables to solve differential equations (Previously on the Calculus option now on HL)**

a) A worksheet (docx file) with some questions separating variables to solve differential equations. Markscheme here.

**12. Solving differential equations by substitution (Previously on the Calculus option now on HL)**

a) A worksheet (docx file) with some questions using substitution to solve homogenous differential equations. Markscheme here.

**13. Solving differential equations by the integrating factor method (Previously on the Calculus option now on HL)**

a) A worksheet (docx file) with some questions using the integrating factor to solve differential equations. Markscheme here.

**14. Maclaurin series (Previously on the Calculus option now on HL)**

a) A worksheet (docx file) with some questions using the Maclaurin series. Markscheme here.

**Investigation resources for Paper 3 [Higher Level]**

- Old IA investigations

**Standard Level**

**[Links removed – hopefully the IB will provide these resources elsewhere]**

(a) All SL IA investigations from 1998 to 2009 : This is an excellent collection to start preparations for the new Paper 3.

(b) Specimen investigations: These are 8 specimen examples of IA investigations from 2006 with student answers and annotations.

(c) SL IA investigations 2011-2012: Some more investigations with teacher guidance.

(d) SL IA investigations 2012-2013: Some more investigations with teacher guidance.

(e) Koch snowflakes: This is a nice investigation into fractals.

**Higher Level **

(a) All HL IA investigations from 1998 to 2009: Lots more excellent investigations – with some more difficult mathematics.

(b) HL IA investigations 2011-2012: Some more investigations with teacher guidance.

(c) HL IA investigations 2012-2013: Some more investigations with teacher guidance.