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Discussion in 'Mathematics' started by hammad0, Oct 22, 2012.

  1. if 2x + y = 10 and A = xy then what is the value of A ????
  2. if 2x + y = 10 and A = xy then what is the value of A ????
  3. how old are you? is this your homework?
  4. i m 21 but m very poor in maths
  5. are you a teacher? why do you need to know this?
  6. DM

    DM New commenter

    You won't be able to find the value of A but you can express A in terms of just x or just y.
    If 2x + y = 10 then y = 10 - 2x
    so A = xy = x (10 - 2x)
    You could eliminate x in a similar way.
    I can see why florapost is probing, this is a peculiar query.
  7. PaulDG

    PaulDG Occasional commenter

    Looks like a "solving problems with graphs" question to me.

    Been set it as homework?
  8. ah DM - now that's interesting
    i eliminated x and found A = f(y)
    i wonder what that says about us [​IMG]
  9. but my friend !
    in my book the value of 'A' is given as 12.5
    i mean in (Answer section)
    i have to solve it
  10. DM

    DM New commenter

    Then, old chum, you have not given us the entire question.
  11. and you still haven't explained why you're doing this
    florapost - stuck on one note this evening
  12. Is it this one? [​IMG]
    cyolba, stuck in the middle with you :)
  13. Nazard

    Nazard New commenter

    Is there any chance, then, that the actual question was "What is the _smallest_ value of A?" ?

    In which case you can either draw the graph of A = 10x - 2x^2 (which is just an expansion of the brackets that DM provided for you earlier in the thread) and find that the minimum point is where x=2.5, or you can differentiate and, because you know from the shape of the graph that when the derivative = 0 you will have a minimum point you can solve 10-4x=0 to give x=2.5

    Then y follows.

    Does this help?

    Others have already asked, but if you told what course you were following (eg elementary calculus) then it would help to give an appropriately tailored answer ...
  14. this question was brought from ((New additional Mathematics)) book
    its for GCE 'O' level
    the topic name:Higher derivatives and Application
    topic no:17
    Exercise:17.3 Q:3
    m doing practice from this book for my (CIE A level) exam

  15. DM

    DM New commenter

  16. Guish

    Guish New commenter

    Or post here

  17. If the book says that A = 12.5,
    then the question is asking for the maximum value of A which is infact 12.5, since
    A = x(10-2x).
    There is something missing in the question that you wrote!! unless you are playing games!
  18. m not playing any game :(

  19. thank youuuuuuuu ssooooooo much
    u have made my night


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