If Q is a tautology is PQ a tautology too If so whySolutiong

If Q is a tautology, is PQ a tautology too? If so, why?

Solution

given Q  is a tautology

so Q is always true

now consider the truth table of AB

A B AB

T T T

T F F

F T T

F F T

So AB is true if B is true

similarly PQ is true if Q is true

so PQ is a tautology since PQ is a tautology