Page 30 - 新思维数学学生用书8 样章

2.1 Constructing expressions

You write the mystery number multiplied by itself as n × n or simply n . Tip
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n + 5 and 3n are called linear expressions because the variable is only
multiplied by a number. n + 5 is the same
n is not a linear expression because the variable is multiplied by itself. as 1 × n + 5.
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Worked example 2.1

Tyler thinks of a number, x. Write an expression for the number Tyler gets when he

a doubles the number and subtracts 3
b divides the number by 3 and adds 2
c adds 2 to the number, then multiplies by 4.

Answer

a 2x − 3 Multiply x by 2, then subtract 3. Write 2 × x as 2x.
b x + 2 Divide x by 3, then add 2. Write x ÷ 3 as .
x
3 3
c 4(x + 2) Add 2 to x, then multiply the answer by 4. Write x + 2 in brackets to
show this must be done before multiplying by 4.

Exercise 2.1

1 Copy and complete these sentences. Use the words from the cloud. solved
In the ................... 4x + 9, x is a .................... coefficient
4x and 9 are ................... of the expression. terms

4 is the ................... of x. 9 is a .................... variable
The expression is not equal to anything so cannot be .................... constant
2 a Tanesha has a box that contains x DVDs. expression

Choose the correct expression from the cloud that shows
the total number of DVDs she has in the box when
i she takes 2 out x x + 2
ii she puts in 2 more 2

iii she takes out half of the DVDs x − 2 2x
iv she doubles the number of DVDs in the box.
b Tanesha starts with 12 DVDs in the box. Work out how

many she will have for Question 2a, parts i to iv.

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