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How did the book get to (7.12)?

  1. Feb 20, 2014 #1
    1. The problem statement, all variables and given/known data

    I am reading through a chapter on the multivariable chain rule, and I was able to follow the steps up until 7.12. It is photographed below.

    2. Relevant equations


    3. The attempt at a solution

    Of the terms listed, I am able to FOIL the operators out, understanding that, because the statement has operators, that commutativity is not necessarily true. From this, I was able to get, of the 7 terms listed in 7.12, terms 1, 3, 5, 7. I do not know where they get terms 2, 4, 6 from.

    What am I missing in my multiplication of operators?
  2. jcsd
  3. Feb 20, 2014 #2
    Don't forget the product rule; 1/r is a function of r, and c and s are functions of θ.
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