Integers — Class 6 Maths (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 6 Mathematics, Term 3 — Chapter 2. Numbers below zero and the number line.
1. About this chapter
This chapter introduces integers — positive and negative whole numbers — their representation on the number line, ordering, the additive inverse, and addition and subtraction.
2. What are integers?
- Integers are … −3, −2, −1, 0, 1, 2, 3 … — the positive numbers, the negative numbers and zero.
- Negative integers are used for ideas like below zero, below sea level, loss and owing money.
3. The number line and ordering
- On the number line, 0 is the centre; positive integers lie to the right and negative integers to the left.
- A number to the right is greater: so −5 < −2 < 0 < 3.
4. Additive inverse, addition and subtraction
- The additive inverse of an integer is the number that adds with it to give 0: the additive inverse of 4 is −4 (and of −7 is 7).
- Adding integers: same signs → add and keep the sign; different signs → subtract and take the sign of the larger. (−3) + 5 = 2; (−3) + (−5) = −8.
- Subtracting an integer = adding its additive inverse: 4 − (−2) = 4 + 2 = 6.
5. Worked examples
Example 1. Which is greater, −8 or −3? −3 is to the right of −8 → −3 is greater.
Example 2. Find the additive inverse of −9. 9 (since −9 + 9 = 0).
Example 3. Evaluate 6 + (−10). Different signs → 10 − 6 = 4, sign of larger (10) → −4.
6. Exercises (Samacheer Kalvi)
- Represent −4, 0 and 2 on the number line.
- Arrange in ascending order: 3, −5, 0, −1, 4.
- Write the additive inverse of (a) 7 (b) −12.
- Find: (a) (−6) + 9 (b) (−4) + (−7) (c) 5 − (−3).
- The temperature was −2 °C and rose by 5 °C. Find the new temperature.
7. Common mistakes
- Mistake: Thinking −8 is greater than −3. Fix: On the number line, the number further right is greater, so −3 > −8.
- Mistake: Treating subtraction of a negative as subtraction. Fix: Subtracting a negative is the same as adding: 4 − (−2) = 4 + 2.
- Mistake: Wrong sign when adding different signs. Fix: Subtract and take the sign of the larger number.
8. Quick revision
- Term 3 · Ch 2 · integers.
- Integers: … −2, −1, 0, 1, 2 …; negatives to the left of 0, positives to the right; right = greater.
- Additive inverse adds to 0 (inverse of 5 is −5).
- Same signs: add and keep sign; different signs: subtract, take sign of larger; subtracting a negative = adding.
