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Example 9 - Prove that root 3 is irrational - Chapter 1 - Irrational numbers

Example 9 - Chapter 1 Class 10 Real Numbers - Part 2
Example 9 - Chapter 1 Class 10 Real Numbers - Part 3
Example 9 - Chapter 1 Class 10 Real Numbers - Part 4

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Example 9 Prove that 3 is irrational. We have to prove 3 is irrational Let us assume the opposite, i.e., 3 is rational Hence, 3 can be written in the form / where a and b (b 0) are co-prime (no common factor other than 1) Hence, 3 = / 3 b = a Squaring both sides ( 3b)2 = a2 3b2 = a2 ^2/3 = b2 Hence, 3 divides a2 So, 3 shall divide a also Hence, we can say /3 = c where c is some integer So, a = 3c Now we know that 3b2 = a2 Putting a = 3c 3b2 = (3c)2 3b2 = 9c2 b2 = 1/3 9c2 b2 = 3c2 ^2/3 = c2 Hence 3 divides b2 So, 3 divides b also By (1) and (2) 3 divides both a & b Hence 3 is a factor of a and b So, a & b have a factor 3 Therefore, a & b are not co-prime. Hence, our assumption is wrong By contradiction, 3 is irrational

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.