# Example 14 - Chapter 14 Class 11 Mathematical Reasoning

Last updated at Dec. 8, 2016 by Teachoo

Last updated at Dec. 8, 2016 by Teachoo

Transcript

Example 14 Check whether the following statement is true or false by proving its contrapositive. If x, y ∈ Ζ such that xy is odd, then both x and y are odd. Let p : xy is odd. q : both x and y are odd. The given statement is of the form it p then q i.e. p ⇒ q We have to check the validity of statement by contrapositive method. i.e. x and y are not odd & prove that is false i.e. prove that xy is not odd Now consider x & y are not odd i.e. x & y are even let x = 2n for same n, m ∈ Z & t = 2m Calculate xy = 2n × 2m if n, m ∈ Z = 4mn ⇒ nm ∈ Z = 2 (2 m n) ⇒ 2n m ∈ Z This show xy is even ⇒ xy is not odd ⇒ p is false ⇒ ~ p Hence ~ q ⇒ ~ p

Proving True - By Contrapositive

Chapter 14 Class 11 Mathematical Reasoning

Concept wise

- Statements
- Writing negation of statements
- Negation - Checking if true or not
- Finding Compound Statement
- Words 'And' & 'Or'
- Inclusive and exclusive or
- Quantifiers
- Contrapositive and converse
- If then
- If and only if
- Proving not true/false (by giving counter examples)
- Proving True - If and only if
- Proving True - By Contrapositive
- Proving True - By Contradiction
- Necessary and sufficient condition

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.