Page 8 - 新思维数学活动用书9 样章

1.2 Standard form

12 This Venn diagram shows all the numbers from a number line. B
A is the set of integers. B is the set of rational numbers. A
Copy the diagram and put each of these numbers in the correct place.
5
25 5.5 5 25 3 25
19
13 a If n = 20, find the value of
(
i n + 2 ii n − 2 iii n + 2)( n − 2) .

b Sofia says:

If n is an integer,
then ( n+2)( n－2) is
also an integer.

Is Sofia correct? Give some evidence to support your answer.

1.2 Standard form

Exercise 1.2

Key word
Focus standard form

1 Write these numbers in standard form.
a 2 600 000 b 920 000 000 c 462 000 d 20 800 000

2 Write these numbers in standard form.
a 55 000 b 55 million c 640 million d 406 million
3 These numbers are in standard form. Write each number in full.
a 5.3 × 10 4 b 5.38 × 10 7 c 7.11 × 10 11 d 1.331 × 10 8
4 A light year is the distance light travels in one year.
One light year is 9 460 000 000 000 km.

Write this distance in standard form.

7