Finding the inverse of a function

A function is  a special mapping where every element from set A (the domain) is mapped exactly to one element in set B (the range).

Domain refers to the x values that the function occupies, and range referring to the y values. For example: A function of 1/x does not have any values of x=0 or y=0 because these are the asymptotes of the equation.

Therefore... for every value of A to map to set B, the domain and range must specify this i.e:
 Domain:   x ∈ R, x ≠0
 Range:       y ∈ R, y ≠0

 Now every element from set A maps to elements in set B and the equation f(x) = 1/x {x ∈ R, x ≠0} and is now a function.

It is regarded as a one-to-one function because every element of the range comes exactly from one element in the domain.

Finding the inverse of a function:

The example function will be: 2x²-7

1.Set the function equal to y:

y=2x²-7

2.Rearrange to make x the subject:

y=2x²-7

y+7=2x²

0.5(y+7)=x²

x=√(0.5(y+7))

3.Replace (x=) with (f^-1(x)=) and replace (y) with (x)

x=√(0.5(y+7))

f^-1(x)=√(0.5(y+7))

f^-1(x)=√(0.5(x+7))

The inverse of a function graphically, is literally just f(x) reflected in the line y=x.

For example:

"https://en.wikipedia.org/wiki/Inverse_function#/media/File:Inverse_Function_Graph.png"

As shown above, the function just gets reflected in the line y=x to give the inverse function.

Exams Approaching - Revision Tips

1. Don't overdo it;
The best way is to plan your time efficiently and go for a mix between quality and quantity.

2. Everyone revises different
You need to find the way that revision best suits you; whether it be mind maps, or spider diagrams. Don't worry if you are different to the way that your mates study, different things work for different people.

3. Take breaks
It's proven that studying in short 45 minute periods is much more beneficial than hours of solid revision, so make sure you plan your rest time too!

4.Make a timetable
Doing so will allow you to maximise the time in your day and will actually give you more free time. If you continue to muck about with choosing what to study, you are wasting time that collectively adds up to a lot of unused, wasted time.

5. Food, Water, Exercise
Three components that are absolutely crucial to exam success. Without these the body cannot function as well as it could have done, and puts you to a disadvantage. Keep hydrated, full of energy and ready to take on the world!

6. Sleep
Having enough sleep will help you concentrate better and keep your focus while studying.

7. Balanced Life
The more you study the better you'll be. However remember to go out and treat yourself for the hard work you've been doing.

8. Start studying early
The earlier you start, the more time you have to learn all your content meaning, the earlier you start, the better you'll do!

Good Luck!

Checking Validity of Functions and Inverse Functions

Sometimes it can be hard to tell whether or not a graph or equation is a valid function or not. Here are some simple steps to checking this:

Horizontal line test: If a straight line can be drawn horizontally that crosses the graph in two places, then this function is called a many to one function. This is only true if a values of x are plotted. However, when finding the inverse of this function, the graph will be reflected in y=x and will no longer abide by the Horizontal line test, but the Vertical line test.

Vertical Line test: If a straight, vertical line can be drawn that crosses the graph in two places, then this is 'one to many' which is not a function. 

1) Vertical line test true = not a function.

2) Horizontal line test true = many to one function

    Horizontal line test true = inverse will not be a function.

Long Division VS Remainder Theorem

Both methods may be used to divide polynomials by a factor such as (x-3), however take different steps in reaching the end goal.


Long Division

As shown, the factor (x-3) is multiplied by a term to create a new expression that can be subtracted from the original polynomial. This is repeated until the polynomial reaches 0 in which case there is no remainder, or it cannot be divided further, in which case there is a remainder.
The terms are then collected and the remainder is stated as above: 29/(x-3) where the remainder is divided by the divisor.

The Remainder Theorem

This method in my opinion takes longer. The idea is that a polynomial (Ax^3 + Bx^2 + Cx + D) is created and using substitution, these values of ABCD can be calculated. First assume there is a remainder i.e. +D.
We then let x =3. This allows us to work out the value of D.
Then we let x =0. This allows us to work out the value of C.
We then compare coefficients i.e. the coefficient (LHS) of x^3 is 1. Therefore the coefficients of all the x^3's on the RHS must also equal to 1. Therefore A=1.
With x^2 LHS equals 1. Therefore all of the x^2 terms i.e. -3Ax^2 + Bx^2 must also equal 1. This can be used to work out the remaining values of ABCD and the remainder stated, divided by the divisor i.e. 29/(x-3).

Mathematical Proof By Induction

Proof by induction is just one type of mathematical proof that follows a main method:

1) BASIS:
Prove the general statement is true for n = 1

2) ASSUMPTION:
Assume the general statement is true for n = k

3) INDUCTIVE:
Show that the general statement is then true for n = k + 1

4) CONCLUSION:
The general statement is then true for all positive integers, n.


And an example question:

(BASE STEP)
Prove by the method of mathematical induction that for n is a set of positive natural numbers:

Sum from r=1 to n; (2r-1) = n^2

n=1; LHS = 2(1)-1 = 1
        RHS = 1^2 = 1
Therefore true for n = 1.

(ASSUMPTION)
Assume that the summation formula is true for n = k;

Sum from r=1 to k (2r-1) = k^2

With n = k + 1, terms the summation formula becomes:

(INDUCTIVE STEP)
Sum from r = 1 to (k+1) of (2r-1) = 1+3+...+(2k-1)+(2k+1)
                                                   
= k^2                 + (2k+1)
=k^2 + 2k + 1
=(k+1)^2

Therefore summation formula is true when n = k + 1

(CONCLUSION)
If the summation formula is true for n = k then it is shown to be true for n = k + 1. As the result is true for n = 1, it is now also true for all n  ≥ 1 and n is a set of positive natural numbers by mathematical induction.

TIPS
When trying to prove the inductive step, a very good idea is to write the formulae out that you have derived^^ i.e. (k^2 + 2k + 1) and then write out the other part of the formula (k^2) but replacing k with the summation i.e. k+1; therefore you get (k+1)^2.
Then it is much easier to prove the formulae as you have (k^2 + 2k + 1) and now it is just a matter of rearranging formulae to get (k+1)^2; which in this case is very easy, but helps a lot when the questions become harder.

Cambridge CUSU Shadowing Scheme

A few weeks ago I attended the Cambridge CUSU Shadowing Scheme, which allowed me to stay at Kings College Cambridge for 3 days, where I would sit, eat, study and socialise with the current undergraduates at the College.

Obviously I shadowed Mathematics while I was there; attending 3rd and 4th year lectures such as Set Theory and Geometric Group Theory (very complex maths).

One of the first things that I was so astonished by when I arrived was the amount of people that rode bicycles! There were hardly any cars on the road, as they were filled with cyclists. Now I realise that Cambridge, being a relatively small campus was mostly accessible by bicycle and therefore it would be much more efficient for people to cycle; for increased speed and saving money.

Meeting 1st, 2nd, 3rd and even 4th year students from Cambridge; it has really opened my eyes to the actual size of mathematics and how inexperienced I am. I feel that there is infinite amounts to be learnt and still many more ideas to be revealed.

I liked the idea that it was also possible for students in the first year, and so on to attend lectures that they are not currently studying. For example: my mentor is currently in his first year at Cambridge, but attended lectures that were in the third and even fourth year (that is degree mathematics!). I felt that this; along with the absolutely enormous library that the Colleges had; really allowed students to maximise their productiveness in study time and allow them to develop an understanding of the topic that far outweighed the average.

From what I had gathered, I also found that the connection between students that were not at the same college was great. As they all have the motivational drive to work hard in their given subjects, it was easy for people to spark conversation and discuss complex theories that they had been recently studying.

Concluding; Cambridge is awesome!

A Level Maths Lecture - Dr Piers Bursill-Hall

Earlier today, I attended a very interesting A Level Maths Lecture with the speakers Dr Piers Bursill-Hall The talks were very interesting and gave a wide range of insights into the uses and application of mathematics; from how the Heliocentric Model was proposed and developed.

Dr Piers Bursill-Hall

Being Cambridge University's most entertaining Maths Lecturer; his talk was very engaging. He commented on how "Copernicus was wrong, and that even his mathematics was wrong." 

Firstly, he announced that Copernicus was most definitely not the first person to invent the Heliocentric Model, and that really he was one of many to have looked at it by his time. It was said that Copernicus also did not only have one theory on the model; but actually he had two. He stated that the first model was that the physical representation of the solar system was with the Sun in the centre, and that all the planets orbited around the Sun, with the stars furthest away. Then there was the second model that went into mathematical detail into how the planets and moons were not actually in a singular elliptical orbit at all, but orbits upon orbits upon orbits. It was said that in the model there was roughly 150 different orbits! 

Finally, the Romans had started to believe in the idea of Christianity. However it was easy to make a link between both the Sun being in the centre of the Solar System and God. An analogy was described that if you imagine a man living in a cave. He has lived there for his whole life and has not been exposed to much light at all. Suddenly the man is exposed to the outdoors and he becomes blinded by the suns light. As the man becomes to adapt to the new surroundings and be able to see things, we will see shapes, flowers, grass and so on. Eventually he will be able to see the sun, and that the sun is the last thing that he will see because it brings light to everything else and it is the most powerful being. This related the centre of the Heliocentric Model to be the most powerful, and now the link between God and the Sun had been made.