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gate 1990 maths propositional logic

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hi sir,

In above question I made truth table and checked for equivalence but I am not able to get  tautology in any of the options.

Plz help.

regards

Piyush

1 Answer

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ANS: a

P->Q=~PvQ....(1)

Q->R=~QvR....(2)

P->R=~PvR....(3)

add 1,2 then we get (Pv~R) [De-morgan's low]

then add with (3) so and get 1 as answer.other options cannot satisfy so option a is the answer
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