Page 10 - 新思维数学学生用书7 样章
P. 10
1.1 Adding and subtracting integers
Subtraction is the inverse operation of addition.
The inverse of 3 is −3. The inverse of −5 is 5.
To subtract an integer, you add the inverse.
You can draw a number line to help you.
Worked example 1.2
Work out:
a 2 − 6 b −4 − −3 c 2 − −4
Answer
a 2 − 6 = 2 + −6 Add the inverse of 6. The inverse of 6 is −6.
–6 –5 –4 –3 –2 –1 0 1 2 3
2 − 6 = 2 + −6 = −4
b −4 − −3 = −4 + 3 Add the inverse of −3. The inverse of −3 is 3.
–5 –4 –3 –2 –1 0 1 2
−4 − −3 = −4 + 3 = −1
c 2 − −4 = 2 + 4 = 6
0 1 2 3 4 5 6 7 8
Worked example 1.3
Estimate the answers to calculations by rounding the numbers.
a −48 + −73 b 123 − 393 c 6.15 − −4.87
Answer
a −48 + −73 is approximately This is rounding to the nearest 10.
−50 + −70 = −120
b 123 − 393 is approximately This is rounding to the nearest hundred.
100 − 400 = −300
c 6.15 − −4.87 is approximately This is rounding to the nearest whole number.
6 − −5 = 6 + 5 = 11
9
