Real Numbers
Gujarat Board · Class 10 · Mathematics
Quick revision notes for Real Numbers — Gujarat Board Class 10 Mathematics. Key concepts, formulas, and definitions for last-minute revision.
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The Fundamental Theorem of Arithmetic
- Every composite number can be expressed as a product of prime numbers, and this factorisation is UNIQUE (except for the order of factors).
- This is called the Fundamental Theorem of Arithmetic because it is the most basic and important fact about integers.
- The theorem was first recorded in Euclid's Elements (Proposition 14, Book IX) and correctly proved by Carl Friedrich Gauss in 'Disquisitiones Arithmeticae'.
Revisiting Irrational Numbers and Proofs
- A number is irrational if it CANNOT be written as p/q, where p and q are integers and q ≠ 0.
- Examples of irrationals: √2, √3, √5, √7, π, 0.10110111011110...
- The proof that √2 is irrational uses a method called 'Proof by Contradiction'.
Step-by-Step: Proof that √2 is Irrational
- STEP 1 — Assume the Opposite: Assume that √2 is rational.
- STEP 2 — Write in Fraction Form: Since √2 is rational, we can write √2 = a/b, where a and b are integers, b ≠ 0, and HCF(a, b) = 1 (i.e., a and b are coprime).
- STEP 3 — Square Both Sides: Squaring gives 2 = a²/b², so a² = 2b².
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