27
Positive and negative numbers. Integers
Textbook, pp. 123–126
GoalUnderstand positive and negative numbers and integers; record real-life quantities with them.
New words
positive number · musbat sonnegative number · manfiy sonintegers · butun sonlarzero · nol
Explanation
The natural numbers 1, 2, 3, ... are also called positive numbers. Numbers to the left of zero are negative numbers: −1, −2, −3, ... A negative number has a “−” sign in front. Natural numbers, their negatives and zero together form the integers. Zero is neither positive nor negative. Negative numbers occur often in life: temperatures below 0 °C, places below sea level, debts. For example, if the air is 7 degrees below zero, we write −7 °C.
Worked examples
A diver is 12 m below sea level: −12 m. A pigeon 30 m above the ground: +30 m.
Among −8, 0, 12, 1/2 the integers are −8, 0 and 12. The number 1/2 is not an integer.
Class activity
“Thermometer”: a vertical thermometer is drawn on the board. Pupils mark temperatures such as −5 °C and +8 °C and discuss which is colder.
Practice
1
The temperature is 7 degrees below zero. Write it as a number.
-7
2
Which of −8, 0, 12, 1/2, −3 are integers?
−8, 0, 12, −3
3
You have 5,000 soms and your friend owes 3,000 soms. Express your friend's money as a number.
−3000
4
Why is 0 neither positive nor negative?
Zero is the starting point that separates positive and negative numbers; it is on neither side of itself.