Page 17 - 新思维数学活动用书8 样章

2 Expressions, formulae and equations

2.2 Using expressions and formulae

Exercise 2.2 Key words

formula
Focus

A formula is a mathematical rule that connects two or more quantities. formulae
It can be written in letters or words. The plural of formula is formulae. substitute
Before you start using formulae, you need to be able to substitute
numbers into expressions. Tip

1 Match each expression with its correct value when x = 6. A is x + 3 =
The first one is done for you: A and iii
6 + 3 = 9. This
A x + 3 i 13 matches with iii.
B x − 5 ii 4

C 7 + x iii 9 Tip
D 10 − x iv 12
x + y = 4 + 3 = ?
E 2x v 3
x
F vi 1 Tip
2
2
y = y × y
2 Work out the value of each expression when x = 4 and y = 3.
a x + y b x − y c y 2

3 Complete the working to find the value of each expression Tip
when x = 6 When you
a 2x + 1 (Work out the multiplication substitute
2 × x + 1 = 2 × 6 + 1 before the addition) numbers into

= 12 + 1 an expression
= or formula, you
b 3x − 1 (Work out the multiplication must use the
3 × x − 1 = 3 × 6 − 1 before the subtraction) correct order
= − 1 of operations:

= brackets, indices,
c 2x 2 (Work out the indices before the division or
2 × x = 2 × 6 2 multiplication) multiplication,
2
= 2 × 36 addition or
= subtraction.

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