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Math Help - TI89Ti: Inaccurate intercepts

  1. #1
    Junior Member
    Joined
    Sep 2008
    From
    Mesnil, Mauritius
    Posts
    30

    TI89Ti: Inaccurate intercepts

    f(x)= \sqrt{3x+4} and g(x)= x^3.
    (fog)(x)=(gof)(x)

    \sqrt{3x^3+4}= (\sqrt{3x+4})^3

    If I plot \sqrt{3x^3+4}- (\sqrt{3x+4})^3=0,
    and do a F5,2 (Zero), I get xc=-962025 and yc=-.02286

    In fact, if I plot another graph, y2=0, and find the intersection, I get the correct answer (-1,0)

    Why is there an inaccuracy in the Zero function?

    Besides, my TI89Ti takes around 4 seconds to plot this graph. How can I speed up the graphing? I have disabled pretty-print, set the coordinates format to rectangular (in polar form, I noticed, the calc takes more time), disabled Discontinuity Detection (F3,Graph->F1,Tools,9:Format).

    Any ideas?
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  2. #2
    Newbie
    Joined
    Dec 2008
    Posts
    6

    Hi

    In my Ti-89T (OS 3.10)
    it gave me the correct answer though.
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