﻿ Class 11 NCERT Math Solution
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TOPICS
Formulae

Rule-1 :-
```  If p and q are mathematical statements, then in order to show that the statement “p and q” is true, the following steps are followed.
Step-1 : Show that the statement p is true.
Step-2 : Show that the statement q is true.
```
Rule-2 Statements with “Or”:-
```  If p and q are mathematical statements, then in order to show that the statement “p or q” is true, one must consider the following.
Case 1 : By assuming that  p is false, show that q must be true.
Case 2 : By assuming that q is false, show that p must be true.
```
Rule-3 Statements with “If-then”:-
```  In order to prove the statement “if p then q” we need to show that any one of the following case is true.
Case 1 : By assuming that p is true, prove that q must be true.(Direct method)
Case 2 : By assuming that q is false, prove that p must be false.(Contrapositive method)
```
Rule-4 Statements with “if and only if ” :-
```  In order to prove the statement “p if and only if q”, we need to show.
(i)  If p is true, then q is true and
(ii)  If q is true, then p is true
```
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