Читать книгу The Physics and Technology of Diagnostic Ultrasound: A Practitioner's Guide - Robert Gill - Страница 9

An equation is a mathematical statement in which the left and right sides are equal.

It can contain numbers, symbols and functions. Symbols are letters standing for numbers (for example x, y). It is common to use a standard symbol for a particular physical quantity (e.g. f for the ultrasound frequency) but this is purely a convention. Suffixes can be used to allow the same letter to be used for related quantities (e.g. c1 and c2 to represent the propagation speed in the first and second tissue).

Examples of functions are trigonometric functions like sine, cosine and tangent (abbreviated sin, cos and tan respectively). Note that 5y means the same as (5 × y), i.e. 5 multiplied by y.

An equation can be rearranged so that you can evaluate one quantity as a function of all the others. This is achieved by adding or subtracting the same amount from both sides or multiplying or dividing each side by the same amount (all of which leave the equation still true). The left and right hand sides can also be interchanged. For example:

and: