Thread: maths in a program

  1. #1
    Registered User
    Join Date
    Jan 2002

    maths in a program

    Hi guys.
    I know this isn't code but maths to go into a program, I need to know which is right.

    I have a couple of formulae which need rearranging:

    1) Make r the subject of.
    a = 2pi(r + h)

    first multiply out the bracket 2pir + 2pih = a

    then subtract 2pih from both sides 2pir = a - 2pih

    now divide both sides by 2pi r = a - 2pih / 2ip ( this is the answer that I have ).

    2) make x the subject of.
    5(x + 2) = y

    first multiply out the bracket 5x + 10 = y

    then subtract 10 from both sides 5x = y - 10

    now divide both sides by 5 x = y - 10 / 5 ( stop here with this answer or do the maths on the right hand side giving x = y / 5 - 2 ) where do I stop with the answer.

    in question 1 I stopped as soon as the required subject was on its own but in question 2 i got the required subject on its own and then proceeded to simplify the maths on the rhs (which way is correct)

    THANKS for the help (learner wanting to be a master).

  2. #2
    Registered User
    Join Date
    Sep 2001
    Firstly, you went the long way around to get 'r' and 'x' the subjects.

    a= 2pi(r + h)
    a/2pi = r+h
    r = a/2pi -h

    5(x + 2) = y
    x + 2 = y/5
    x = y/5 - 2

    Simple. But if you understand the other way better stick to that. Second, if 'x' is the subject to be, go all the way, don't stop halfway through.

  3. #3
    kwigibo's answers are correct, whereas yours are missing parentheses. Your answers should be:
    r = (a - 2pih) / 2pi
    x = (y - 10) / 5,
    which are equal to kwigibo's.

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