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angela210793

  • 2 years ago

Inverting matrices :S

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  1. angela210793
    • 2 years ago
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    |dw:1328979083071:dw|

  2. amistre64
    • 2 years ago
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    cofactor, transpose, divide by determinant

  3. amistre64
    • 2 years ago
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    or swap some stuff in a 2x2

  4. angela210793
    • 2 years ago
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    let me try it and u tell me if i have solved it right ok???

  5. satellite73
    • 2 years ago
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    yeah easy method for 2 by 2

  6. amistre64
    • 2 years ago
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    forgot to transpose lol

  7. amistre64
    • 2 years ago
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    last time .... and i forgot to use the checkerboard +- correctly a b c d cofactors to: d -c -b a transposes to d -c -b a then divide by determinate maybe!! lol

  8. angela210793
    • 2 years ago
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    is this right? |dw:1328979427660:dw|

  9. TuringTest
    • 2 years ago
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    for invertible 2x2 matrices\[A=\left[\begin{matrix}a & b \\ c & d\end{matrix}\right]\]\[A^{-1}=\frac1{\det A}\left[\begin{matrix}d & -b \\ -c & a\end{matrix}\right]\]looks good angela

  10. FoolForMath
    • 2 years ago
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    Trick: Swap the diagonal element and change the sign of off-diagonal ones

  11. amistre64
    • 2 years ago
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    thats what i was trying for lol

  12. angela210793
    • 2 years ago
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    I think cofactors will be d -b -c a

  13. amistre64
    • 2 years ago
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    b is not its own cofactor

  14. FoolForMath
    • 2 years ago
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    2 days back I learned a super fast way for doing 3x3 matrices

  15. amistre64
    • 2 years ago
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    cofactor is the determinate of the submatrix

  16. amistre64
    • 2 years ago
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    the submatrix of b is c in this case

  17. angela210793
    • 2 years ago
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    Thanks guys :) How abt a 4x4 matrix????

  18. satellite73
    • 2 years ago
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    \[ M = \left[ {\begin{array}{cc} x & y \\ z & w \\ \end{array} } \right] \] M = \begin{array}{cc} x & y \\ z & w \\ \end{array} \] \[ M^{-1}= \frac{1}{xw-yz}\left[ {\begin{array}{cc} w& -y \\ -z & x \\ \end{array} } \right] \]

  19. FoolForMath
    • 2 years ago
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    For this one the answer is\[ \begin{bmatrix} \cos x & \sin x \\ -\sin x & \cos x \end{bmatrix} \]

  20. amistre64
    • 2 years ago
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    same process just messier and more apt to computers

  21. satellite73
    • 2 years ago
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    god it took me a long time to write that

  22. angela210793
    • 2 years ago
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    well am not a computer....O.o

  23. amistre64
    • 2 years ago
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    then youll have to get a monk

  24. TuringTest
    • 2 years ago
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    Cofactors is a good way to get bigger determinants if the matrix has some number of zeros in it

  25. satellite73
    • 2 years ago
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    finding inverse of 4 by 4 by hand is long process, use a machine

  26. FoolForMath
    • 2 years ago
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    I like to use reduce row-echelon for method for 4x4

  27. satellite73
    • 2 years ago
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    i like to use maple

  28. TuringTest
    • 2 years ago
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    if it's like 0022 1536 0739 0297 you can expand the cofactors along the first column and you only need to take one determinant, all the minors are zero except for 1

  29. angela210793
    • 2 years ago
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    ahhhhaaaa...I got it.....Thank you all ^^

  30. amistre64
    • 2 years ago
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    a b c d e f g h i j k l m n o p +fgh - egh +efh -efg jkl ikl ijl ijk nop mop mnp mno etc ........... then transpose; and divide off the original determinate

  31. angela210793
    • 2 years ago
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    Amistre u lost me....wht did u do in there??

  32. amistre64
    • 2 years ago
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    the cofactor is the determinants of the submatrixes

  33. amistre64
    • 2 years ago
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    its an algorithm

  34. angela210793
    • 2 years ago
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    I'm sorry but all i know for algorithms is the name....I have no idea wht they r

  35. amistre64
    • 2 years ago
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    |dw:1328980027433:dw|

  36. angela210793
    • 2 years ago
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    i know wht submatrices r...

  37. amistre64
    • 2 years ago
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    an algorithm is a means of operating on data multiplication is an algorithm; division is an algorithm its a process that aids us

  38. amistre64
    • 2 years ago
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    it sorts the data into a usable form that we can maniipulate to our own devious devices :)

  39. TuringTest
    • 2 years ago
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    yeah, all that procedural stuff the process you use in long division for example computers do all problems with algorithms, they never think 'outside the box' so to speak

  40. angela210793
    • 2 years ago
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    OMG!!! I'm going to fail :(

  41. TuringTest
    • 2 years ago
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    ? why?

  42. angela210793
    • 2 years ago
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    cause i have to colve 100 probs and i have solved only 10...yay :P

  43. angela210793
    • 2 years ago
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    and my stupid teacher doesn't know to explain at all -_-

  44. sasogeek
    • 2 years ago
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    |dw:1328980182059:dw|

  45. sasogeek
    • 2 years ago
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    i know nothing about 4x4 matrices but i know there's something to do with + - + something somewhere dealing with cofactors and it should look something like this... not sure

  46. sasogeek
    • 2 years ago
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    i think that's what amistre did when he drew "a" and wrote "sub" in the box

  47. TuringTest
    • 2 years ago
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    that will get you the determinant of a 4x4 if you want the inverse I would probably use the row reduction thing

  48. angela210793
    • 2 years ago
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    I kinda got it...

  49. TuringTest
    • 2 years ago
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    this is a good site http://tutorial.math.lamar.edu/Classes/LinAlg/FindingInverseMatrices.aspx

  50. sasogeek
    • 2 years ago
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    Angela, you need to get it, u don't need to "kinda" get it... that won't get u far lol :P

  51. angela210793
    • 2 years ago
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    Leave me alone geek...:P I got microeconomy,finance,communication to study too -_-

  52. sasogeek
    • 2 years ago
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    welcome to university :)

  53. angela210793
    • 2 years ago
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    yea right :'( I wish i never started it :P

  54. Akshay_Budhkar
    • 2 years ago
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    i wish i start it soon! @angela

  55. angela210793
    • 2 years ago
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    tht's cause u don't know yet wht it feels like to be in univ :p

  56. Akshay_Budhkar
    • 2 years ago
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    if i dont go to univ i wont be great :P

  57. angela210793
    • 2 years ago
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    u may go to univ and still not b great Akshay

  58. Akshay_Budhkar
    • 2 years ago
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    i will be its a guarantee as it is "ME" :P

  59. angela210793
    • 2 years ago
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    Ehe :P

  60. Akshay_Budhkar
    • 2 years ago
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    u got matrices in economics?

  61. angela210793
    • 2 years ago
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    yea we have maths...and we're getting too much information in just one lecture..teacher never shows an example to us and we're all like: ''Is tht chinese??''

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