Page 23 - 新思维数学活动用书7 样章

2 Expressions, formulae and equations

13 Kai has two pieces of wood. The lengths of the pieces of wood are shown in the diagram.

8a + 15 2b – 3c
Write an expression for:
a the total length of the pieces of wood

b the difference in the lengths of the pieces of wood.
14 p and q are whole numbers, such that p + q = −2 and pq = −8. Also p > q.
a Sadie thinks that p = −12 and q = 10. Explain why Sadie is wrong.
b Work out the values of p and q.

2.2 Using expressions and formulae

An expression is a statement that contains letters and sometimes Key words
numbers but has no = sign.
For example: p x + 2 n − 3 4m formula

You can substitute numbers into an expression to work out the value of substitute
the expression.
For example, the value of x + 2 when x = 5 is 5 + 2 = 7.
A formula is a statement that contains letters and sometimes numbers Tip

and has an = sign. Substitute the x
For example: A = 2p y = x − 2 v = 5n − 3 R = m + k for the number
5 and then work
out 5 + 2.
Exercise 2.2

Focus

1 For each of these statements, write the letter E if it is an expression

or write the letter F if it is a formula. The first two have been done
for you.
a 8h E c 9u + 3 e G = 2x + y
b v = 9u F d m = 4 + n f b − c
Tip
2 Work out the value of x + 6 when: In part a,
a x = 1 b x = 2 c x = 3 d x = 4

x+ 6 = 1 + 6 =

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