Page 55 - 新思维数学学生用书7 样章

2 Expressions, formulae and equations

Summary checklist

I can understand and solve equations.
I can write equations and solve them.

2.6 Inequalities

In this section you will … Key words

• use letters to represent a range of numbers. advantages

disadvantages
In this unit so far, you have used a letter to represent an unknown number. inequality
You can also use a letter and an inequality to represent an open interval.
The inequality symbols used to represent open intervals are: inequality

< meaning ‘is less than’ symbols
> meaning ‘is greater than’. integer
Example: The inequality x > 4 means that x can be any number greater negative infinity
than 4. open interval

The inequality y < 7 means that y can be any number less than 7. positive infinity
Each inequality represents an open interval. In the first interval, x cannot be
equal to 4. In the second interval, y cannot be equal to 7.
You can show an open inequality on a number line like this:

x > 4
2 3 4 5 6 7
The arrow pointing to the right shows that x can be any number above 4 and Tip

continues towards positive infinity.
You use an open

y < 7 circle for < and
4 5 6 7 8 9 10
> inequalities.
The arrow pointing to the left shows that y can be any number below 7 and
continues towards negative infinity.

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