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sara12345 Group Title

Logic

  • one year ago
  • one year ago

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  1. sara12345 Group Title
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    |dw:1348907509327:dw|

    • one year ago
  2. sara12345 Group Title
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    if 'a', then 'b' : a-> b

    • one year ago
  3. sara12345 Group Title
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    is that correct ?.. can i write teh same as, only if 'b', then 'a' ?

    • one year ago
  4. badreferences Group Title
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    Are you asking if you can reverse "if A, then B" to "if B, then A"?

    • one year ago
  5. sara12345 Group Title
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    no, the thing troubling me is "only if"

    • one year ago
  6. badreferences Group Title
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    That doesn't sound right. "Only if" B still has many things that aren't A.

    • one year ago
  7. sara12345 Group Title
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    actually i dont get "if and only if", im trying to understand it by breaking it down to "if" and "only if"

    • one year ago
  8. sara12345 Group Title
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    may i knw why it doesnt sound right to you, it does sound right to me

    • one year ago
  9. badreferences Group Title
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    But... a square is a kind of a rectangle.

    • one year ago
  10. sara12345 Group Title
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    |dw:1348907860375:dw|

    • one year ago
  11. badreferences Group Title
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    "A square cannot be a rectangle"?

    • one year ago
  12. sara12345 Group Title
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    excuse me, my question is different, plz look at the diagram what im asking

    • one year ago
  13. sara12345 Group Title
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    only if its b, then only it can be a

    • one year ago
  14. UnkleRhaukus Group Title
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    • one year ago
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  15. badreferences Group Title
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    "In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles." "In geometry, a square is a regular quadrilateral. This means that it has four equal sides and four equal angles (90-degree angles, or right angles)." So a square shares all the properties of a rectangle, but has the additional condition that it's regular. So all squares are rectangles.

    • one year ago
  16. sara12345 Group Title
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    a doesnt have any possibility outside b

    • one year ago
  17. badreferences Group Title
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    No, but just because it's B doesn't necessarily mean it's A.

    • one year ago
  18. badreferences Group Title
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    Replace A with "it rained last night" and B with "the grass was wet the next morning".

    • one year ago
  19. badreferences Group Title
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    There are many ways for the grass to be wet the next morning (dew, sprinklers), even if it raining last night necessarily means that the grass is wet next morning.

    • one year ago
  20. sara12345 Group Title
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    @UnkleRhaukus you got me correctly! 3rd point in ur snapshot says it

    • one year ago
  21. badreferences Group Title
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    Ahh, okay, the third point. I thought you were saying something else. My bad.

    • one year ago
  22. sara12345 Group Title
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    its okay... i dont get "if and only if" could you walk me through slowly plz

    • one year ago
  23. sara12345 Group Title
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    ive understood "only if" i guess, whats "if and only if", i mean i knw it means, a iff b is same as a->b, b->a

    • one year ago
  24. sara12345 Group Title
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    but why it is called "if and only if" is confuses me

    • one year ago
  25. UnkleRhaukus Group Title
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    \[\begin{array}{ccccc}\phi&\psi&\phi\Rightarrow\psi&\phi \Leftarrow\psi&\phi\Leftrightarrow\psi\\ \hline \\T&T&T&T&T\\T&F&F&T&F\\F&T&T&F&F\\F&F&T&T&T\end{array}\]

    • one year ago
  26. badreferences Group Title
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    Unkle, is it just me, or is "only if B then A" different from "A iff B"?

    • one year ago
  27. badreferences Group Title
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    only if B then A is different from A if and only if B.

    • one year ago
  28. sara12345 Group Title
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    im familiar with xnor truth table, but still why its called "if and only if" should we break it into two : 1) if, 2) only if

    • one year ago
  29. sara12345 Group Title
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    a iff b break as : if a then b, a only if b ?

    • one year ago
  30. zzr0ck3r Group Title
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    @sara12345 do you understand if a then b?

    • one year ago
  31. UnkleRhaukus Group Title
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    if and only if \(\Leftrightarrow\) iff

    • one year ago
  32. sara12345 Group Title
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    yes, i understood iff also, only the "phrase" is confusing me

    • one year ago
  33. zzr0ck3r Group Title
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    I think I'm confused about what your asking. Sorry.

    • one year ago
  34. sara12345 Group Title
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    sorry, like a iff b can i break it into 2 pieces : 1) if a then b, 2) a only if b ?

    • one year ago
  35. sara12345 Group Title
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    the two broken statements, do they cover completely "a iff b" ?

    • one year ago
  36. sara12345 Group Title
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    il start over.

    • one year ago
  37. UnkleRhaukus Group Title
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    these statements say the same thing 1) if a then b, 2) a only if b _______

    • one year ago
  38. sara12345 Group Title
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    ohh yea they say same thing, a->b

    • one year ago
  39. UnkleRhaukus Group Title
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    to meant the same as a iff b switch the letters around in one of them

    • one year ago
  40. sara12345 Group Title
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    so hw can iu break it meanigfully

    • one year ago
  41. sara12345 Group Title
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    a "if and only if " b : a <--> b a "if" b : b->a a "only if" b : a->b i guess now i have it working in above

    • one year ago
  42. sara12345 Group Title
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    i see there is lot of difference between, "if" and "only if"

    • one year ago
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