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Thread: Simplify i

  1. #1
    Junior Member fluffy_penguin's Avatar
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    Simplify i



    $\displaystyle = (i^3)^7$
    $\displaystyle =-i$

    Also can someone help me fill in my i chart that my teacher started...

    $\displaystyle i^1 = ?$
    $\displaystyle i^2 = -1$
    $\displaystyle i^3 = i^2 * i = -i$
    $\displaystyle i^4 = i^2 * i^2 = 1$
    $\displaystyle i^5 = i^4 * i = i$
    $\displaystyle i^6 = i^3 * i^3= ?$
    $\displaystyle i^7 = i^4 * i^3= ?$
    $\displaystyle i^8 = i^4 * i^4= ?$
    $\displaystyle i^9 = i^5 * i^4= ?$
    $\displaystyle i^10 = i^5 * i^5= ?$
    $\displaystyle i^11 = i^5 * i^6= ?$
    $\displaystyle i^12 = i^5 * i^7= ?$
    $\displaystyle i^13 = i^5 * i^8= ?$
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by fluffy_penguin View Post


    $\displaystyle = (i^3)^7$
    $\displaystyle =-i$
    that's incorrect $\displaystyle i^{21} = i \cdot i^{20} = i \cdot \left( i^2 \right)^{10} = i $

    see here, they have a nice list of rules, it will also help you check the answers for your chart
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Also can someone help me fill in my i chart that my teacher started...

    $\displaystyle i^1 = ?$
    $\displaystyle i^2 = -1$
    $\displaystyle i^3 = i^2 * i = -i$
    $\displaystyle i^4 = i^2 * i^2 = 1$
    $\displaystyle i^5 = i^4 * i = i$
    $\displaystyle i^6 = i^3 * i^3= ?$
    $\displaystyle i^7 = i^4 * i^3= ?$
    $\displaystyle i^8 = i^4 * i^4= ?$
    $\displaystyle i^9 = i^5 * i^4= ?$
    $\displaystyle i^10 = i^5 * i^5= ?$
    $\displaystyle i^11 = i^5 * i^6= ?$
    $\displaystyle i^12 = i^5 * i^7= ?$
    $\displaystyle i^13 = i^5 * i^8= ?$
    just reuse the previous values.

    for instance, $\displaystyle i^6 = i^3 \cdot i^3$

    so look up in your chart for $\displaystyle i^3$, we see that $\displaystyle i^3 = -i$

    thus, $\displaystyle i^6 = i^3 \cdot i^3 = -i \cdot -i = i^2 = -1$


    continue the same way. and use the link i gave you to check your answers
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  4. #4
    Junior Member fluffy_penguin's Avatar
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    Thanks.
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  5. #5
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    Hello, fluffy_penguin!

    Can someone help me fill in my chart that my teacher started...

    $\displaystyle \begin{array}{ccccccc}i^1 & = & & & & &{\color{blue}i} \\i^2 & = & & & & & {\color{blue}\text{-}1} \\i^3 & =& \;\,i^2\cdot i \;&= & (\text{-}1)i &=& {\color{blue}\text{-}i} \\i^4 &=& \;\,i^3\cdot i \;& = & (\text{-}i)(i) &=& {\color{blue}1}\end{array}$
    $\displaystyle \begin{array}{ccccccc}i^5 &=& i^4\cdot i &=& (1)(i)& = & {\color{red}i} \\i^6 &=& i^5\cdot i &=& (i)(i ) &=& {\color{red}\text{-}1} \\i^7 &=& (i^6)(i) &=&(\text{-}1)(i) &=& {\color{red}\text{-}i} \\i^8 &=& (i^7)(i) &=& (\text{-}i)(i) &=& {\color{red}1}\end{array}$
    Don't you see the pattern?

    The successive powers are: .$\displaystyle i,\;-1,\;-i,\;1$ . . . . . over and over.



    Simplify: .$\displaystyle i^{21}$
    We know that: .$\displaystyle i^4 \,=\,1$

    So we have: .$\displaystyle i^{21} \:=\:i^{20}\cdot i \;=\;(i^4)^5\cdot i \;=\;(1)^5\cdot i \;=\;i $

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