• @Pipoca
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    91 year ago

    It’s BE(D=M)(A=S). Different places have slightly different acronyms - B for bracket vs P for parenthesis, for example.

    But multiplication and division are whichever comes first right to left in the expression, and likewise with subtraction.

    Although implicit multiplication is often treated as binding tighter than explicit. 1/2x is usually interpreted as 1/(2x), not (1/2)x.

    • @CheesyFox
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      11 year ago

      a fair point, but aren’t division and subtraction are non-communicative, hence both operands need to be evaluated first?

      • @Pipoca
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        1 year ago

        1 - 3 + 1 is interpreted as (1 - 3) + 1 = -1

        Yes, they’re non commutative, and you need to evaluate anything in parens first, but that’s basically a red herring here.

    • @unoriginalsin
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      Afaraf
      11 year ago

      It’s BE(D=M)(A=S). Different places have slightly different acronyms - B for bracket vs P for parenthesis, for example.

      But, since your rule has the D&M as well as the A&S in brackets does that mean your rule means you have to do D&M as well as the A&S in the formula before you do the exponents that are not in brackets?

      But seriously. Only grade school arithmetic textbooks have formulas written in this ambiguous manner. Real mathematicians write their formulas clearly so that there isn’t any ambiguity.

      • @Pipoca
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        1 year ago

        That’s not really true.

        You’ll regularly see textbooks where 3x/2y is written to mean 3x/(2y) rather than (3x/2)*y because they don’t want to format

        3x
        ----
        2y
        

        properly because that’s a terrible waste of space in many contexts.

        • @unoriginalsin
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          Afaraf
          11 year ago

          You’ll regularly see textbooks

          That’s what I said.

          • @Pipoca
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            01 year ago

            You generally don’t see algebra in grade school textbooks, though.

            • @unoriginalsin
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              Afaraf
              11 year ago

              12 is a grade. I took algebra in the 7th grade.

              • @Pipoca
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                1 year ago

                Grade school is a US synonym for primary or elementary school; it doesn’t seem to be used as a term in England or Australia. Apparently, they’re often K-6 or K-8; my elementary school was K-4; some places have a middle school or junior high between grade school and high school.

                • @unoriginalsin
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                  Afaraf
                  11 year ago

                  I don’t know why you’re getting lost on the pedantry of defining “grade school”, when I was clearly discussing the fact that you only see this kind of sloppy formula construction in arithmetic textbooks where students are learning the basics of how to perform the calculations. Once you get into applied mathematics and specialized fields that use actual mathematics, like engineering, chemistry and physics, you stop seeing this style of formula construction because the ambiguity of the terms leads directly to errors of interpretation.

                  • @Pipoca
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                    11 year ago

                    Sure, the definition of grade school doesn’t really matter too much. Because college texts are written in ways that violate pemdas.

                    Look, for example, at https://www.feynmanlectures.caltech.edu/I_45.html

                    For example, if f(x,y)=x2+yx, then (∂f/∂x)y=2x+y, and (∂f/∂y)x=x. We can extend this idea to higher derivatives: ∂2f/∂y2 or ∂^2f/∂y∂x. The latter symbol indicates that we first differentiate f with respect to x, treating y as a constant, then differentiate the result with respect to y, treating x as a constant. The actual order of differentiation is immaterial: ∂2f/∂x∂y=∂2f/∂y∂x.

                    Notice: ∂^2f/∂y∂x is clearly written to mean ∂^2f/(∂y∂x).