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Math Help - Need help with Factoring and Solving Equations.

  1. #1
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    Post Need help with Factoring and Solving Equations.

    Hi! Ive been trying to do these problems for a while and Im stumped. I finished 13 problems and fully understand them , but I don't know how to do these problems. It would be nice if you could write each step out or the answer at the very least. Or hints or tips, like which theorem or something to use. Shortcuts.

    1. P(x) = 5x + 2kx^4 + 4x^3 - 5k
    P(x)/2x+4 has a remainder of 3, find k.

    2. f(x) = -2x^4 + ix^3 - 2kx^2 - x + 3
    Find k given that (x + 1 + i) is a factor

    I dont even know how to do 1 and 2.

    is there any short cuts?

    Thanks for answering my questions. I really don't understand these problems. I mean I do, but I want to know shorter ways since everything takes so long.
    I dont know when to use synthetic division, factor theorem, etc.
    I need help
    Last edited by Chris L T521; January 10th 2011 at 11:18 PM. Reason: dispersing questions from original thread into separate ones
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  2. #2
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    Hi donaldmax, welcome to the forum.

    Before your next post please review the forum rules as there is a number of them you have breached.

    Quote Originally Posted by donaldmax View Post

    1. P(x) = 5x + 2kx^4 + 4x^3 - 5k
    P(x)/2x+4 has a remainder of 3, find k.
    \displaystyle 2x+4 = 0 \implies x=-2

    Therefore \displaystyle P(-2) = 5(-2) + 2k(-2)^4 + 4(-2)^3 - 5k = 3

    Finish him off, kind regards,
    Last edited by pickslides; January 10th 2011 at 10:19 PM. Reason: *sp
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  3. #3
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    Exclamation number 1 and 2

    for number 1
    What does p(x)/2x+4 mean?
    its like dividing the p(x)?
    O_O
    u told me to do that.
    i found that k = 5/3. is that the answer? do i multiply anything else?


    and for number 2

    do i plug in (1-i) and then solve it?
    or is there more steps? like doing
    (x+1+i)(x+i-i) then do that
    then plug into
    original equation
    find roots/
    and then plug roots into that?
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  4. #4
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    Quote Originally Posted by donaldmax View Post
    u told me to do that.
    i found that k = 5/3. is that the answer? do i multiply anything else?

    No need for any further multipication.


    Quote Originally Posted by donaldmax View Post

    and for number 2

    do i plug in (1-i) and then solve it?
    or is there more steps? like doing
    (x+1+i)(x+i-i) then do that
    then plug into
    original equation
    find roots/
    Solve

    \displaystyle f(-i-1) = -2(-i-1)^4 + i(-i-1)^3 - 2k(-i-1)^2 -(-i-1) + 3 = 0
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  5. #5
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    how did you get -i-1?
    and this is factor theorem right?
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  6. #6
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    Yep,

    If P(a) = 0 then x-a is a factor
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