Sunday 17 March 2013

Important points Chapter 2 book 1


Logical statements are also called propositions
Negation is unairy operation.
Conditional is equivalent to contrapositive.
Converse is equivalent to inverse.
Tautology means ⇾always true.
Absurdity ⇾ always false.
Contingency ⇾either true or false.

MCQ:
(p⇾q) ⇾(∼q⇾∼p) is:
a)    Tautology
b)   Absurdity
c)    Contingency
d)   None of these

Don’t draw the table to check it. You are not provided much time to draw a table for this type of MCQs. First check the conditions carefully.
As conditional is equivalent to contrapositive so it is a tautology. (a)

Residue classes:
In residue class 4:
1)   0 is identity.
2)   3 is the inverse of 1.
3)   2 is the inverse of 2.
4)   1 is the inverse of 3.
Same is in the case of other residue classes depending upon the class.


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