CBSE · Class 9 · Mathematics · Chapter 3

The World of Numbers

Trace the evolution of numbers from early counting and zero to integers, rational numbers, irrational numbers, and the real number system.

7 lessons 80 min
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Lessons in this chapter

  1. 1The Dawn of MathematicsBefore calculators did the thinking, people first had to invent the numbers.
  2. 2The Revolution of Śhūnya: When Nothing Became SomethingZero entered as “nothing” and became one of mathematics’ biggest celebrities.
  3. 3Integers: Expanding the HorizonNegative numbers arrived when counting only what you had was no longer enough.
  4. 4Filling the Spaces: Fractions and Rational NumbersFractions prove that numbers do not have to be whole to be useful.
  5. 5Irrational NumbersSome numbers refuse to end, repeat, or fit into a fraction—decimal rebels.
  6. 6Real Numbers: Decimals and Cyclic PatternsEvery real number gets a place on the line, even when its decimal refuses to behave.
  7. 7Chapter Summary and PracticeSee whether the entire number family still seems rational.
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