Page 29 - 新思维数学学生用书8 样章

2 Expressions, formulae and equations

A formula is a set of instructions for working something out.

It is a rule written using letters or words.
The plural of formula is formulae.
People use formulae in everyday life to work out all sorts of things.
An employer may use a formula to work out how much to pay the people who work for them. For

example, they could use the formula P = R × H, where P is the pay, R is the amount paid per hour and
H is the number of hours worked.
Doctors may use a formula to assess a person’s health. For example, they could use a formula to find
the person’s body mass index (BMI).

This formula is: BMI = mass , where the person’s mass is measured in kilograms and their height
height 2
is measured in metres.
If a person’s BMI is too high or too low, the doctor may ask them to lose or put on weight, to make
them healthier.

2.1 Constructing expressions

In this section you will … Key words

• use letters to represent numbers coefficient
• use the correct order of operations in algebraic constant
expressions

• use words or letters to represent a situation. equivalent
expression

You can write an algebraic expression by using a letter to represent an linear expression
unknown number. term

In the expression 3n + 8 there are two terms. 3n is one term. The other unknown
term is 8. variable
The letter n is called the variable, because it can have different values.
The coefficient of n is 3, because it is the number that multiplies the

variable.
The number 8 is called a constant.
Example:
Let n represent a mystery number.

You write the number that is 5 more than the mystery number as n + 5
or 5 + n.
You write the number that is three times the mystery number
as 3 × n or simply 3n.

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