# General Discussions

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Math

skittles234  posted on Oct 07, 2010 7:29:42 PM - Report post

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So I was bored one day in math class (Calc ab) and as many people do I pulled out my trusted TI-83 and was graphing random things. And I came across an enigma.

I graphed "log(X)/sin(x^cos(X))" (in radians) with the window set to
"Xmin=0
Xmax=10"

I then set the window to normal (Xmin=-10) and I got an error. And I thought why? Because the log of a negative doesn't exist, so I graphed "log(abs(X))/sin(X^cos(X))" with the window set to normal. It gave me the same error

So after a little bit of work, I discover that when X=-1 (for example) sin(-1^cos(-1)) = -.115+.904i so that made sense. But shouldn't the same thing happen after X=2pi?

Any explanation would help greatly.

DABhand  posted on Oct 08, 2010 6:14:55 PM - Report post

AUTHOR
Maybe it was because you can actually divide by 0 with that equation, and we all know it means the end of the universe if you try.

Neo7  posted on Oct 13, 2010 7:18:10 AM - Report post

MODERATOR
Set the domain for 0 >= x >= 2*pi

Division by zero shouldn't matter when graphing an equation as the calculator will either insert a hole or an asymptote where the equation would be undefined. It doesn't know now to deal with non-real values though.

[Edited by Neo7, 10/13/2010 7:19:56 AM]

TalonKarde  posted on Oct 13, 2010 7:58:58 AM - Report post

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jimmy buffet said it best in the song of the same name "Math Sucks."

skittles234  posted on Oct 13, 2010 1:56:57 PM - Report post

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quote:
originally posted by Neo7

Set the domain for 0 >= x >= 2*pi

Division by zero shouldn't matter when graphing an equation as the calculator will either insert a hole or an asymptote where the equation would be undefined. It doesn't know now to deal with non-real values though.

[Edited by Neo7, 10/13/2010 7:19:56 AM]

But that's the thing, it lets you graph the equation even when the domain is set to 0>=x>=10, rather than 0>=x>=2*pi. The only time it doesn't let you is when the domain is -10>=x>=10.

Toastman  posted on Oct 14, 2010 8:48:35 AM - Report post

ELITE
quote:
originally posted by skittles234

quote:
originally posted by Neo7

Set the domain for 0 >= x >= 2*pi

Division by zero shouldn't matter when graphing an equation as the calculator will either insert a hole or an asymptote where the equation would be undefined. It doesn't know now to deal with non-real values though.

[Edited by Neo7, 10/13/2010 7:19:56 AM]

But that's the thing, it lets you graph the equation even when the domain is set to 0>=x>=10, rather than 0>=x>=2*pi. The only time it doesn't let you is when the domain is -10>=x>=10.

Ugh. I understand what you're talking about. This isn't good. College is learning me things.

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