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Need Help Memorizing Contrapositives!

Posted: Mon Aug 08, 2011 6:41 pm
by stupidcha
My brain is going mush from all the studying. This is what I did in a problem moments ago. Pg 208 in LGB

K -> X
then
X -> K

This is wrong I believe. I don't know why though...

So if ~X, then ~K?

Thus B? answer turns out to be A and I understand the reasoning behind it but my brain seems to like to do the problem like the way shown above.

Does anyone have an easy way to remember these contrapositives? Seems like they aren't really sticking with me.
Thank you!

Re: Need Help Memorizing Contrapositives!

Posted: Mon Aug 08, 2011 6:42 pm
by Ruxin1
stupidcha wrote:My brain is going mush from all the studying. This is what I did in a problem moments ago. Pg 208 in LGB

K -> X
then
X -> K

This is wrong I believe. I don't know why though...

So if ~X, then ~K?

Thus B? answer turns out to be A and I understand the reasoning behind it but my brain seems to like to do the problem like the way shown above.

Does anyone have an easy way to remember these contrapositives? Seems like they aren't really sticking with me.
Thank you!
Image

Re: Need Help Memorizing Contrapositives!

Posted: Mon Aug 08, 2011 6:51 pm
by stupidcha
wait what? flame? hmm...

Re: Need Help Memorizing Contrapositives!

Posted: Mon Aug 08, 2011 6:54 pm
by minnbills
Well flame or not here you go:

Just flip and negate.

If A, then B

becomes

If not B, then not A

Re: Need Help Memorizing Contrapositives!

Posted: Wed Aug 10, 2011 8:57 pm
by cking2014
A -> B

contrapositive:

~B -> ~A

just flip and negate each side, best way to remember!!