Posers and Puzzles

Posers and Puzzles

  1. Donationastevenson
    i wish i was BOB!!!!
    Larkfield!(kent, uk)
    Joined
    19 Oct '01
    Moves
    14933
    15 Jun '03 19:22
    can someone help me here, this was in my GCSE maths paper and i didnt have a clue how to solve it..

    prove that 20x + x squared = 400 (prove means u dont answer it im guessing)
  2. Norway
    Joined
    19 Dec '02
    Moves
    483
    17 Jun '03 00:211 edit
    I cannot see how you're supposed to prove that:
    20x + x^2 = 400

    However, it is possible to solve it, and find x (I suppose that's the purpose of this task):

    20x + x^2 = 400
    x^2 + 20x + 100 = 500
    (x + 10)^2 = 500
    x + 10 = [+/-]sqrt(500)
    x = [+/-] 10sqrt(5) - 10

    If you'd like, you can say:
    x = 10([+/-]sqrt(5) - 1)

    [+/-] -- plusminus-thingy (\pm in (La)TeX) πŸ™‚
  3. Joined
    07 Jul '03
    Moves
    87
    10 Jul '03 15:24
    maybe it was

    prove that 20x squared divided by x^2 = 400
  4. Standard membergenius
    Wayward Soul
    Your Blackened Sky
    Joined
    12 Mar '02
    Moves
    15128
    11 Jul '03 12:42
    Originally posted by astevenson
    can someone help me here, this was in my GCSE maths paper and i didnt have a clue how to solve it..

    prove that 20x + x squared = 400 (prove means u dont answer it im guessing)
    if you solve it, then you are proving it, are you not? but would that not be possible for any equation of that form? i.e. 463x+2x^2=547, albeit that x will not always be in interget...?
  5. R.I.P.
    Joined
    21 Dec '01
    Moves
    8578
    12 Jul '03 21:38
    Maybe it is possible if the x was something on the lines of .9975124???? (I run out digits on my calcπŸ˜€)
  6. R.I.P.
    Joined
    21 Dec '01
    Moves
    8578
    12 Jul '03 21:451 edit
    Did in excel instead x= 0.997512422417805 πŸ˜‰
  7. Joined
    26 Apr '03
    Moves
    26510
    12 Jul '03 23:21
    Originally posted by astevenson
    can someone help me here, this was in my GCSE maths paper and i didnt have a clue how to solve it..

    prove that 20x + x squared = 400 (prove means u dont answer it im guessing)
    For the wording of that question to make sense, they must have given you the value of X or made you work it out in an earlier part of the question.
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