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!

Simple Complex number

  1. Aug 11, 2011 #1
    how to solve sqrt(-8.3)sqrt(1 - i8)?


    i try to solve it.. but got the wrong answer..

    sqrt(-8.3)sqrt(1 - i8) = sqrt[(8.3i^2)(1 - 8i)]
    = sqrt (8.3i^2 - 66.4i)
    = 2.88i + 8.15

    the answer should be.. 5.41 + i6.13
     
  2. jcsd
  3. Aug 11, 2011 #2

    eumyang

    User Avatar
    Homework Helper

    Here's a problem (in bold). You can't take the square root of a sum/difference separately. In other words,
    [itex]\sqrt{a + b} \ne \sqrt{a} + \sqrt{b}[/itex]
     
  4. Aug 11, 2011 #3
    then... what should i do..? i got stuck there...
     
  5. Aug 11, 2011 #4

    eumyang

    User Avatar
    Homework Helper

    Assuming you want just the principal square root, consider this: if there is a complex number a + bi such that
    [itex]\sqrt{z} = a + bi[/itex],
    then it makes sense that
    [itex]z = (a + bi)^2[/itex].

    First simplify the expression so that there is one square root. You sort of did that here (in bold):
    ... but there is a sign mistake. Also, forget about rewriting a negative as i2 in your 1st step.

    Whatever is under the square root is your z. Take this:
    [itex]z = (a + bi)^2[/itex]
    and expand the right-hand side. Equate the real number parts and the imaginary number parts. You'll end up with 2 equations and 2 unknowns. Solve for a and b.
     
    Last edited: Aug 11, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Simple Complex number
  1. Complex numbers (Replies: 6)

Loading...