Maths - Equations

Equations

An equation is a mathematical expression with an equals sign in it.

Possible elements of an equation are:

These are explained in following sections.

Solving equations

Once we can solve quadratic equations and simultaneous equations it is tempting to think that we will be able to solve more and more complicated equations by using the same principles but its not always that simple. The quadratic equation:

a x² + b x + c = 0

can be solved using a formula but most polynomial equations don't have formulas to give the solution. Every polynomial with only real or complex coefficients has a complex number solution , this is the fundamental theorem of algebra, but they cannot always be expressed exactly with radicals. To find an approximation to the solution we may have to use numerical methods such as the Newton-Raphson method or Laguerre method.

Generalised reciprocity laws are very complicated algorithms that enable you to get crucial information about some of these more complicated equations. In favorable circumstances, they can be used to prove deep statements about the solution sets of algebraic equations.

An equation does not have to be too complicated to lack a formula, for example:

x5 - x + 1 = 0

Numbers

There are different types of numbers, for instance:

and these numbers may be coded in different ways:

Unless otherwise specified we usually assume that numbers are decimal.

Number theory is a big subject with topics like prime numbers, Galois theory, Fermats last
theorem containing many active ares of mathematical study.

Variables

Sometimes an equation contains a number but we don't yet know its value, or we may want to apply the equation to a range of values.

An example of the first is using x as the unknown, for example,

x + 1 = 3

An example of the second might be an equation of a line:

y = 2 * x + 3

In general we use:

x, y, z for unknowns.

a, b, c for values which are not yet specified.

Binary Operators

The operators:

take the two numbers on either side and replace it by a single number.

Unary Operators

The operators:

apply to the number to the right. '-' inverts the number (subtracts from 0) '+' says the number to the right is positive (the default).

Brackets

When we mix + and * then the answer we get depends on the order that we apply them.

For example

2 + 1 * 3

To clarify this we can put brackets around the operation to be applied first:

(2 + 1) * 3 = 9

2 + (1 * 3) = 5

If we don't specify which has precedence by using bracket then by default * and ÷ have precedence over + and -. So,

2 + 1 * 3 = 5

Functions

A function takes one number and uses it to generate another number. For example the function sin() takes an angle as input and returns the ratio of opposite and hypotenuse in a right angled triangle.


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Correspondence about this page

Book Shop - Further reading.

Where I can, I have put links to Amazon for books that are relevant to the subject, click on the appropriate country flag to get more details of the book or to buy it from them.

flag flag flag flag flag flag Fearless Symmetry - This book approaches symmetry from the point of view of number theory. It may not be for you if you are only interested in the geometrical aspects of symmetry such as rotation groups but if you are interested in subjects like modulo n numbers, Galois theory, Fermats last theorem, to name a few topics the chances are you will find this book interesting. It is written in a friendly style for a general audience but I did not find it dumbed down. I found a lot of new concepts to learn. It certainly gives a flavor of the complexity of the subject and some areas where maths is still being discovered.

 

Terminology and Notation

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