Real Numbers – Class 10 Maths Notes (CBSE / RBSE)

Introduction to Real Numbers, Properties, and Board Exam Important Questions

Real Numbers Mathematics ka ek aisa foundational chapter hai jiske bina Algebra, Geometry, aur Trigonometry jaise important topics ko deeply samajhna possible nahi hota. Class 10 Board Exams (RBSE/CBSE) ke perspective se yeh chapter kaafi zyada scoring mana jata hai, kyunki isme concepts logical hain aur questions ka pattern kaafi predictable hota hai. Agar aap Real Numbers ke concepts ko achhe se samajh lete hain, toh aap 6–8 marks almost sure-shot score kar sakte hain.

Is detailed article mein hum Real Numbers ke har ek concept ko step-by-step explain karenge — definitions se lekar proofs, examples, tricks, aur exam-oriented tips tak — taaki aap board exams mein confident feel karein aur maximum marks achieve kar sakein.

1. What are Real Numbers? (वास्तविक संख्याएँ)

Real Numbers wo sabhi numbers hote hain jinhe hum Number Line par represent kar sakte hain. Matlab jo bhi number kisi na kisi point par number line par exist karta hai, wo Real Number ke category mein aata hai. Real Numbers ke andar do main categories hoti hain:

• Rational Numbers

• Irrational Numbers

Simple shabdon mein kaha jaaye toh:

Real Numbers (R) = Rational Numbers (Q) + Irrational Numbers

Real Numbers ka use sirf textbooks tak limited nahi hota. Real life mein bhi hum inka use rozana karte hain, jaise:

• Temperature measure karne ke liye (positive aur negative values)

• Distance aur length measure karne ke liye

• Money, profit-loss, aur banking calculations mein

Isliye Real Numbers ko Mathematics ka backbone bhi kaha jata hai.

2. Classification of Numbers (Numbers ke Types)

Real Numbers ko properly samajhne ke liye hume pehle number system ki basic classification ko revise karna zaroori hota hai. Neeche har type ko detail mein explain kiya gaya hai:

A. Natural Numbers (N)

Natural Numbers wo numbers hote hain jinse hum counting start karte hain. Ye sabse basic numbers hote hain jo bachpan mein sabse pehle sikhaaye jaate hain.

Definition: Wo numbers jo 1 se start hote hain aur infinity tak jaate hain.

Set Representation: N = {1, 2, 3, 4, 5, …}

Key Point: Natural Numbers ka smallest number 1 hota hai. Isme zero include nahi hota.

B. Whole Numbers (W)

Jab hum Natural Numbers ke group mein zero (0) ko include kar dete hain, tab hume Whole Numbers milte hain.

Set Representation: W = {0, 1, 2, 3, 4, …}

Important Difference: Har Natural Number ek Whole Number hota hai, lekin har Whole Number Natural Number nahi hota. Example ke liye, 0 ek Whole Number hai par Natural Number nahi.

C. Integers (Z)

Integers wo numbers hote hain jinme positive numbers, negative numbers, aur zero — teeno include hote hain.

Set Representation: Z = {…, -3, -2, -1, 0, 1, 2, 3, …}

Real Life Usage: Integers ka use temperature (minus degrees), profit-loss, lift ke floors, aur direction-based problems mein hota hai.

3. Rational vs. Irrational Numbers (Most Important Concept)

Class 10 Board Exams ke liye yeh section sabse zyada important mana jata hai. Proofs, MCQs, aur short-answer questions aksar yahin se aate hain.

Rational Numbers (परिमेय संख्याएँ)

Rational Numbers wo numbers hote hain jinhe hum p/q ke form mein likh sakte hain, jahan:

• p aur q dono Integers hone chahiye

• q ≠ 0 (denominator zero nahi ho sakta)

Examples:

• 1/2

• -5/7

• 4 (kyunki 4 = 4/1)

• 0 (kyunki 0 = 0/1)

Decimal Nature of Rational Numbers:

Rational numbers ka decimal expansion ya toh:

• Terminating hota hai (ruk jaata hai), ya

• Non-Terminating Repeating hota hai (repeat karta hai)

Examples:

• Terminating: 0.5, 2.45

• Repeating: 0.333…, 1.2727…

Irrational Numbers (अपरिमेय संख्याएँ)

Irrational Numbers wo hote hain jinhe p/q ke form mein nahi likha ja sakta. Inka decimal expansion:

• Non-Terminating hota hai

• Non-Repeating hota hai

Examples:

• √2, √3, √5 (imperfect squares ke roots)

• π (Pi)

• 0.1010010001…

4. Fundamental Theorem of Arithmetic

Yeh theorem Class 10 Maths ka ek bahut hi important rule hai, jo HCF aur LCM nikalne ka base provide karta hai.

Statement:

Every composite number can be expressed as a product of prime numbers, and this factorization is unique, except for the order of the prime factors.

Example:

140 ka prime factorization:

• 140 = 2 × 70

• 140 = 2 × 2 × 35

• 140 = 2 × 2 × 5 × 7

Final form: 140 = 2² × 5 × 7

5. HCF and LCM (Prime Factorization Method)

Board exams mein yahan se direct 2–3 marks ke questions aate hain.

HCF (Highest Common Factor): Common prime factors ki smallest power ka product.

LCM (Least Common Multiple): Sabhi prime factors ki greatest power ka product.

Important Formula:

HCF(a, b) × LCM(a, b) = a × b

Solved Example:

Find HCF and LCM of 6 and 20.

6 = 2 × 3 20 = 2² × 5

HCF = 2 LCM = 2² × 3 × 5 = 60

6. Proof of Irrationality (Proof by Contradiction)

Yeh 3 marks ka long-answer question hota hai.

Question: Prove that √2 is irrational.

Steps:

• Assume √2 is rational

• √2 = a/b, where a and b are co-prime

• Square both sides

• Show both a and b divisible by 2

• Contradiction arises

Hence, √2 is irrational.

7. Decimal Expansion Tricks (Without Division)

Agar denominator ke prime factors sirf 2 aur 5 hain, toh decimal terminating hoga. Warna repeating.

Examples:

• 13/3125 → Terminating

• 64/455 → Non-Terminating Repeating

Summary & Exam Tips

• Definitions yaad rakhein

• Proofs step-by-step likhein

• Prime factorization carefully karein

• NCERT exercises zaroor practice karein

Real Numbers ek logical aur scoring chapter hai. Agar concepts clear hain, toh ye chapter aapko board exam mein strong advantage de sakta hai.