Page 25 - 新思维数学学生用书9 样章

2 Expressions and formulae

7 Work out the value of each expression when w = 5, x = 2, y = −8 and z = −1.

a 3(w + x) b x(2w − y) c 3w − z 3 d (2x) 3
e x + y 2 f wx + y g 2(x − z ) h 25 − 2w 2
3
2
2
z
i w + z(2x − y) j (3z) – z 7
4
Activity 2.1

Work with a partner for this activity.
With your partner, choose different values for the letters m and p.
Write three expressions that use m and p, similar to those in Question 6, and work
out the values of your expressions. You can make your expressions as easy or as

difficult as you like but they must have whole number answers.
Write your expressions on a piece of paper, then swap your piece of paper with
another pair of learners in your class.
Work out the values of each other’s expressions. Swap back and mark each other’s

work.
Discuss any mistakes that have been made.

8 This is part of Dai’s homework.
Tip

Question
Use a counter-example to show that the statement A counter-
2x = (2x) is not true (x ≠ 0). example is just
2
2
Answer one example
Let x = 3, so 2x = 2 × 3 = 2 × 9 = 18 and that shows a
2
2
(2x) = (2 × 3) = 6 = 36 statement is not
2
2
2
18 ≠ 36, so 2x ≠ (2x) . true.
2
2
Use a counter-example to show that these statements are not true (x ≠ 0, y ≠ 0).
a 3x = (3x) 2 b (−y) = −y 4 c 2(x + y) = 2x + y
4
2
9 Work out the value of each expression.
a 4(x − 1) + x 3 + 12 when x = 2
2
4
b 3y − 5 + 2y − 21 when y = 3
3
2 y

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