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Math Help - Why we put m sign in demonstrative geometry in theorem?

  1. #1
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    Cool Why we put m sign in demonstrative geometry in theorem?

    Why we put m sign in demonstrative geometry in theorem?
    please tell me while proving theorems
    in statements why there is m symbol before angles like m<ABC + m<BCD=180
    thanks .
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  2. #2
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    I don't remember seeing an "m" before \angle ABC. My guess would be that it stands for "measure", i.e., the magnitude of the angle as opposed to the angle itself as a geometric figure.
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  3. #3
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    Quote Originally Posted by johny123 View Post
    Why we put m sign in demonstrative geometry in theorem?
    in statements why there is m symbol before angles like m<ABC + m<BCD=180
    In axiomatic geometry courses it is written as m\left( {\angle ABC} \right) because m() is a function.
    It is the function that measures angular size.
    Different authors do use slightly different notations.
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    i am in 9th standard , i have seen m symbol before angles but i am confused when/where to put this symbol while proving. please define it .i have my exam in couple of days.

    else i gotta cram all my theorems b4 exam. :P
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  5. #5
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    Quote Originally Posted by johny123 View Post
    i am in 9th standard , i have seen m symbol before angles but i am confused when/where to put this symbol while proving. please define it .i have my exam in couple of days.
    As I said above, that is a matter determined by the author of your text material. Consult your textbook.
    All one can say is that in general m\angle ABC indicates the measure of an angle.
    Whereas, the notation \angle ABC stands for the angle itself: the union of two rays \overrightarrow {BA}  \cup \overrightarrow {BC} .
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    Quote Originally Posted by Plato View Post
    As I said above, that is a matter determined by the author of your text material. Consult your textbook.
    All one can say is that in general m\angle ABC indicates the measure of an angle.
    Whereas, the notation \angle ABC stands for the angle itself: the union of two rays \overrightarrow {BA}  \cup \overrightarrow {BC} .
    Ok one confusion remains ,i have noticed that m symol is everywhere in the statements , but the author put it where there is equal sign(=) like sum of angles e.g m<ABC + m<BCD=90 here is m , where there is congruency of anlges there is no 'm' sign e.g <ABC=~ <BCD (=~ is for congrueny ) :-) so now could please define y is 'm' sign here ?
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  7. #7
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    Quote Originally Posted by johny123 View Post
    where there is congruency of anlges there is no 'm' sign e.g <ABC=~ <BCD (=~ is for congrueny ) :-) so now could please define y is 'm' sign here ?
    If we have m\left( {\angle ABC} \right) = m\left( {\angle BCA} \right) then it follows that \angle ABC \cong \angle BCA, they are congruent.

    It is incorrect to write m\angle ABC \cong m\angle BCA
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  8. #8
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    To add, when we take a sum of two angles, we must use m to convert angles as figures to numbers first and then to add the results. That's why m is used in m\angle ABC + m\angle BCD=90. To say that two angles are congruent, we don't need m since we could say \angle ABC\cong \angle BCD. The latter fact is equivalent to m\angle ABC = m\angle BCD.
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  9. #9
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    Now i got this concept .Thanks Plato and Emakarov for your nice explanation :-)
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