Page 23 - 新思维数学学生用书9 样章

2 Expressions and formulae

Exercise 2.1

1 Copy and complete the workings to find the value of each expression when x = 3 and y = 5.
a x − 2 y = −×25 b x + xy 3 +× c y − 10 x = () 2 10 × 3
3
3
=
5 −
3 5
2
3
y 5
=− = + = − 30
3
= = 5
= −
=
2 Work out the value of each expression when a = −2, b = 3, c = −4 and d = 6.
a b + d b a + 2b c 2d − b d 4b + 2a
e bd − 10 f d + ab g d − a h 20 + b 3
2
2
i ab + cd j bc + a
d

Think like a mathematician

3 Work with a partner to answer this question.
c
a The expression ab − has a value of 24. Write values for a, b, c and d when
d
i a, b, c and d are all positive numbers
ii a, b, c and d are all negative numbers

iii a, b, c and d are a mixture of positive and negative numbers.
b Discuss the methods you used, and the values you found, with other
learners in your class.
c Look at the Thinking and Working Mathematically characteristics.
Which characteristics do you think you have used here?

4 This is part of Pierre’s homework.

Question
Work out the value of each expression when x = –3 and y = –2.
6x
a x + xy b y – y
2
3
Answer
a –3 + –3 × –2 = –9 + 6 b (–2) – 6 × –3 = 8 – –18
3
2
–2 –2
= –3 = 8 – 9
= –1

22