1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

(a+bi)/(x-i)=0 finding x

  1. Feb 21, 2017 #1
    1. The problem statement, all variables and given/known data
    so the equation is 5+3i/(a-i) =0

    i need to find a REAL A so it becomes 0



    2. Relevant equations



    3. The attempt at a solution

    i tried multiplying with its conjugate but it wont take. im completely clueless.
     
  2. jcsd
  3. Feb 21, 2017 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    No way. Please post the complete problem statement . And your attempt at solution in detail. You know how things go at PF
     
  4. Feb 21, 2017 #3
    I need to find a REAL "a" that makes this function 5+3i/(a-i) =0

    maybe i can use trigonometry...
     
    Last edited: Feb 21, 2017
  5. Feb 21, 2017 #4
    There is no single value 'a' can take to give zero. If you multiply, numerator & denominator, by complex conjugate of the denominator to simplify, then will get two equations one for real part & other imaginary. Each requires 'a' to be different values; in fact they are negative reciprocals of each other. So, I'm with BvU in that this cannot be entire problem statement, or there is some other error.
     
    Last edited: Feb 21, 2017
  6. Feb 21, 2017 #5

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Do you perhaps mean

    (5+3i)/(a-i) =0 ?
     
  7. Feb 21, 2017 #6

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    Do you mean
    $$\frac{5 + 3i}{a-i} = 0,$$
    or do you mean
    $$5 + \frac{3i}{a-i}=0?$$
    It makes a great difference.

    Actually, if I read your expression using standard rules for parsing mathematical expressions, what you wrote really is the second one.
     
  8. Feb 21, 2017 #7

    Mark44

    Staff: Mentor

    I am assuming from what you wrote in the title, "(a+bi)/(x-i)=0 finding x", your equation is really this: (5 + 3i)/(a - i) = 0.

    The only way for a fraction or other rational expression to be equal to zero is when the numerator is zero.
     
  9. Feb 21, 2017 #8

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    No, there is a unique ##a## that solves
    $$5 + \frac{3i}{a-i} = 0,$$
    but it is not real.
     
  10. Feb 21, 2017 #9
    (5+3i)/(a-i) =0

    "a" has to be a real number.
     
  11. Feb 21, 2017 #10

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    You can spend the next thousand years looking for a solution, but you will not find one.
     
  12. Feb 21, 2017 #11

    epenguin

    User Avatar
    Homework Helper
    Gold Member

    I'm guessing the real question was ... = 1
     
  13. Feb 21, 2017 #12

    Mark44

    Staff: Mentor

    I agree completely with Ray here. The only way a fraction can be zero is if the numerator is zero. Are you positive that what you have written is the problem that is to be solved?
     
  14. Feb 22, 2017 #13
    nevermind. missunderstood the question i guess. the answer is just solving the a in a+bi and ignoring the i part. trivial question.
     
    Last edited: Feb 22, 2017
  15. Feb 22, 2017 #14

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Is not what I see in post #1. By accident ?
     
  16. Feb 22, 2017 #15
    not an accident. but same kind of problem.
     
  17. Feb 22, 2017 #16

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    repeat my post #2. What do you want to work on ?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted