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Need Help!

  1. Jan 3, 2008 #1
    Hi..
    i hope i wont be boring but ...
    i had some probs this year and i couldnt go to lessions,, so now i'm having a lot of troubles with math...
    At 15 january i have my final exam so i had to learn almost 4 book to pass it...
    I hope that u will help me to solve some math probs....
    (Sorry for my bad english)
    (when i underline a number or something.. i mean that it is conjugated)
    Here are some of them:

    1). we have the complex number z = 1 + 2i. We have to find the complex number
    w the way that finally we will have these :

    Re{w/z} = 2 and Im{z*w} = 2

    2). Solve the equation:

    (2-i)x + (-3+4i)y = -2+3i
    __________________________________________________________________________

    3). Here we have to do With Matrix(matrices)...
    hope u'll understand the way i wrote them....

    We have to find x, y ,u and v so we will have:

    / x-----y+1 \----/ 3 --- x-2 \ -- / y ---- 0 \ -- / 7 --- -3 \
    l----------- l - 2 l ---------- l = l ---------- l - l ---------- l
    \ 0-----u+4 /----\ u --- v+2 / -- \ -v ---- 2 / - \ 4 ----- 9 /

    4). Depending to a parameter, find the matrices rank:


    ----/ 1 1 1 1 \
    A = l 2 a -1 1 l
    ----\ a 4 0 2 /


    ----/ 1 7 17 3 \
    ----l 2 2 a 3 l
    B = l 3 1 1 a l
    ----\ 0 a 10 1 /

    ----/ 1 -2 3 2 a \
    C = l 2 -a 5 -1 7 l
    ----\ 1 -2 1 -8 2 /
    you'll help me a lot if u solve me the probs....

    Bye....
     
    Last edited: Jan 3, 2008
  2. jcsd
  3. Jan 3, 2008 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    You have to learn "almost 4 books" now? When did you learn you would have to pass a final exam?

    Your English is excellent. I am just concerned that you don't seem to have even tried!
    If z= 1+ 2i and w= x+ iy, then [itex]\overline{z}= 1- 2i[/itex] and [itex]\overline{w}= x- iy[/itex]. So [itex]w/\overline{z}= (x+ iy)/(1- 2i)= (x+iy)(1+2i)/((1-2i)(1+2i)= (x-y)/5+ (2x+1)i/5[/itex]. Set the real part of that equal to 2. That gives you one equation for x and y. Do the same with [itex]Im(z\overline{w})= 2[/itex] to get a second equation.

    All right, what have you DONE? Are we to assume that x and y are real numbers? If not there are an infinite number of solutions. You certainly should know that (2- i)x= 2x- ix and (-3+ 4i)y= -3y+ 4yi. That is exactly the same as (2x-3y)+ (-x+ 4y)i= -2+ 3i. If x and y are real numbers, then 2x- 3y= -2 and -x+ 4y= 3.

    Do it! Go ahead and multiply the the matrices on each side and set corresponding terms equal. That will give you 4 equations for x, y, u, and v.

    No, it would not help you one bit for someone else to solve the problems! YOU need to learn to solve them and, all kidding aside, by the time you are taking the final exam, you should already have seen many examples, as well as having solved many of them before. What is the DEFINITION of "rank of a matrix"? Do you know how to find the rank of a matrix by "row reducing" it? Do you know how to "row reduce" a matrix?
     
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