Discussion Problem_(10)

[duck]

Let A and B be two propositions. If we want to disprove the claim that "A if and only if B", it is sufficient to show that
(a)  Both A and B are false
(b)  Both A and B are true
(c)  Exactly one of A and B is true and one is false
(d)  Either show option (a) or option (c) above

[Ayushya Kaul]

Option (c) ?

[Sumit]

option (C)..Exactly one of A and B is true and one is false

[duck]

Correct.. :)

[Mauli]

can u please explainthis
why cantitbe option a or b ?
i am lost in this one..

[duck]

Hi mauli.. :)

Its given A iff B
It means A implies B and B implies A.
Therefore, to disprove "A iff B" , its enough show that one statement is true and another statement is false.
Refer some logic book for more explanation.

[Mauli]

oh i m so sorry duck
i kept ''proving'' it rather than ''disproving''. :p