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Math Help - Basic complex numbers

  1. #1
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    Basic complex numbers

    Hey guys was just wondering if someone could explain why 5i/10i doesnt equal 0.5. My calculator says it is negative 0.5. Should the i's cancel each other out. Please give a detailed explanation, i cant find anything in my text books
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    Quote Originally Posted by sanado View Post
    Hey guys was just wondering if someone could explain why 5i/10i doesnt equal 0.5. My calculator says it is negative 0.5. Should the i's cancel each other out. Please give a detailed explanation, i cant find anything in my text books
    Using the "correct" method (rationalizing the denominator):
    \frac{5i}{10i}

    = \frac{5i}{10i} \cdot \frac{-10i}{-10i} = \frac{-50i^2}{-100i^2} = \frac{50}{100} = \frac{1}{2}
    so you are putting something into your calculator wrong. (Or the calculator needs to be replaced!)

    -Dan
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    Quote Originally Posted by sanado View Post
    Hey guys was just wondering if someone could explain why 5i/10i doesnt equal 0.5. My calculator says it is negative 0.5. Should the i's cancel each other out. Please give a detailed explanation, i cant find anything in my text books
    I have one word for you: BRACKETS!

    You need to key in (5i)/(10i).

    Your calculator will understand 5i/10i to mean 5i/10 and then multiply the result by i, which of course will give -1/2.

    Calculators are very stupid things - they only do exactly what you tell them, often this not what you think you tell them.
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