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Math Help - addition topics in Trig

  1. #1
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    addition topics in Trig

    Hey guys.. new here.. my precalc hw due 2morro.. with dot products and stuff

    Find the Angle theta between the vectors

    19: u = <2i-j> v = -2j

    21: u = <5i+5j> v=<-6i +6i>

    23: u=cos(pi/3)i + sin(pi/3)j v = cos(3pi/4)i + sin(3pi/4)j

    PLEASE HELP PRONTO
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  2. #2
    Jen
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    Quote Originally Posted by jdt214 View Post
    Hey guys.. new here.. my precalc hw due 2morro.. with dot products and stuff

    Find the Angle theta between the vectors

    19: u = <2i-j> v = -2j

    21: u = <5i+5j> v=<-6i +6i>

    23: u=cos(pi/3)i + sin(pi/3)j v = cos(3pi/4)i + sin(3pi/4)j

    PLEASE HELP PRONTO
    The dot product is defined as \vec u \cdot \vec v=|u||v| \cos\theta

    In each of these problems you are given two vectors, we can find the magnitude of each by using this formula,

    For \vec u = <a,b,c>

    |u|=\sqrt{a^2+b^2+c^2}

    We can also find the dot product which is,

    \vec u = <a,b,c> \\\ \vec v = <x,y,z>

    \vec u \cdot \vec v = <a,b,c> \cdot <x,y,z> = ax+by+cz

    Being able to find the dot product and the magnitude we can plug these values into the original equation \vec u \cdot \vec v=|u||v| \cos\theta
    and solve for \theta
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