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Maths Question (sketching)

javjamoll84javjamoll84 Posts: 15,249
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in Advice #1
Hey,

I have a question about graph sketching if anyone could help.

I've been given some exercise sheets to look over and do before a tutorial this week. However I'm having a few problems with this as I've not done maths in 3years and I don't honestly remember much of this aspect of maths tbh.

Basically I need to draw the curves but I just can't figure it out (the the sin part that gets me!)

y= 3sinx - 2x^2 + 3x, where x (is a member of) [0,2]

I'd thought you'd just let it equal 0 then 2. But the 3sinx bit is confusing me - especially with the 3sin2 part.

Am I going about it the right way:confused:

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The other problem I have is with Cartesian forms and sketching it. I've converted it to
x= 3cos15/4(pi) and
y= 3sin15/4(pi)

But how would I draw them? :confused: If anyone could help?

Comments

  • javjamoll84javjamoll84 Posts: 15,249
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    #2
    Ok, I think I'm fine with the Cartesian bit that I asked on the second question. But the first bit :confused: still.
  • varialectiovarialectio Posts: 2,377
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    #3
    "x is a member of [0,2]"

    I've never seen it put quite that way as that's set theory notation indicating, as you say, that x is either 0 or 2 which doesn't seem to make sense in terms of sketching the function. (My maths exams were a very long time ago!) but does it mean for you to have x take a number of values over the range 0 to 2 and then plot the curve.

    X will be in radians, not degrees

    Just checked it by drawing an Excel graph, works fine using 20 points, stepping in 0.1 units. If you're really mean you could get away with 0.2 steps as the curve is fairly smooth.!
  • javjamoll84javjamoll84 Posts: 15,249
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    #4
    Nope, closed brackets. That's how its type on the sheet.

    See if it was <= 2 or something then it'd be easier to understand. But I just don't get it :confused: He briefly went through another example but with the <= which follows that type of notation and I get.

    I may just leave that part and do the rest. Will ask at the tutorial. :)
  • [Deleted User][Deleted User] Posts: 9,455
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    #5
    Urgh, Sin & cos curves, I hated these at a-level maths.

    I just remember always starting with the original sin curve, then each part of the equation making you move, or adapt the curve in some way on the graph.
  • skillerskiller Posts: 963
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    #6
    [0,2] surely means the closed interval where 0 <= x <= 2

    In contrast, (0,2) means the open interval where 0 < x < 2

    Also, you can, for example, have half-open intervals such as [0,2) where 0 <= x < 2
  • javjamoll84javjamoll84 Posts: 15,249
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    #7
    Ahhhhh yes. Hmmm, makes sense now! We even covered open and closed very briefly last semester :o

    So the way I was plotting was correct then?

    I just let X = any number between 0 and 2?
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