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Math Help - scalar product and vector product combined

  1. #1
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    scalar product and vector product combined

    I believe there is a typo in this sentence from a book. Can someeone confirm it?

    "Since a.b is a scaler then (a.b)xc has no meaning and a.(bxc) may be wriiten as a.bxc without ambiguity."
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    Re: scalar product and vector product combined

    Quote Originally Posted by Stuck Man View Post
    I believe there is a typo in this sentence from a book. Can someeone confirm it?
    "Since a.b is a scaler then (a.b)xc has no meaning and a.(bxc) may be wriiten as a.bxc without ambiguity."
    What do you think is a typo?
    I may not care for the way it is written, but I see no typo.
    It says: because (A\cdot B)\times C has no meaning we can write A\cdot B\times C and understand it as A\cdot(B\times C).
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    Re: scalar product and vector product combined

    Why do the brackets say nothing? I find it extremely unusual that brackets are not observed. This is not what I find with a Casio calculator.
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    Re: scalar product and vector product combined

    Quote Originally Posted by Stuck Man View Post
    Why do the brackets say nothing? I find it extremely unusual that brackets are not observed. This is not what I find with a Casio calculator.
    I have no idea what "Why do the brackets say nothing?" could mean.
    These are vectors. A\cdot B is a scalar, a number.
    Cross products are vectors. If t is a scalar and C is a vector then t\times C is meaningless.
    A calculator has absolutely nothing to do with vectors.
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    Re: scalar product and vector product combined

    I thought that t x C was multiplying the vector C by a scaler. It is not the same as tC then? My fx-991 does have a vector mode. I'm not sure now if it does vector products.
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    Re: scalar product and vector product combined

    My calculator does not follow what is being said in that quote from the book. It can do vector products with AxB or AB or A(B).
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    Re: scalar product and vector product combined

    Quote Originally Posted by Stuck Man View Post
    My calculator does not follow what is being said in that quote from the book. It can do vector products with AxB or AB or A(B).
    If A=<1,2,3>~\&~B=<2,3,1> then A\times B=<-7,5,-1>.
    If your calculator does not give that answer, then put it in a drawer and forget it.
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    Re: scalar product and vector product combined

    Quote Originally Posted by Stuck Man View Post
    I thought that t x C was multiplying the vector C by a scaler. It is not the same as tC then? My fx-991 does have a vector mode. I'm not sure now if it does vector products.
    No, the product of scalar t and vector C is denoted by tC. The "x" is reserved for the cross product.
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  9. #9
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    Re: scalar product and vector product combined

    Quote Originally Posted by Stuck Man View Post
    My calculator does not follow what is being said in that quote from the book. It can do vector products with AxB or AB or A(B).
    Taking Plato's example of A= <1, 2, 3> and B= <3, 2, 1>, what does your calculator give for AB or A(B)? There are two kinds of "vector times vector" product (well, three if you include the "exterior product- the exterior product of two n dimension vectors is a n by n tensor.) so the notation "AB" or A(B) is ambiguous.
    Last edited by HallsofIvy; March 30th 2012 at 08:13 AM.
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    Re: scalar product and vector product combined

    I get the vector product, -4i, 8j, -4k for AB, A(B) and AxB with the calculator.

    I have noticed that with the calculator the scaler product has higher precedence than the vector product which has been confusing me. The vector product has precedence in mathematics. I feel that Casio should fix this with later models.
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    Re: scalar product and vector product combined

    Quote Originally Posted by Stuck Man View Post
    I get the vector product, -4i, 8j, -4k for AB, A(B) and AxB with the calculator.
    I have noticed that with the calculator the scaler product has higher precedence than the vector product which has been confusing me. The vector product has precedence in mathematics. I feel that Casio should fix this with later models.
    You are not using that calculator correctly.
    Look at this web page.

    Look at the dot product.
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  12. #12
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    Re: scalar product and vector product combined

    I am. HallsOfIvy copied B wrongly and I used it. I am still questioning why the calculator puts the dot product above the vector product.
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    Re: scalar product and vector product combined

    Once again, if you do the dot product first, you do NOT have two vectors and cannot do the cross product.
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