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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Specialist Mathematics => Topic started by: joechan521 on October 31, 2007, 07:29:16 pm

Title: drawing Arg(z) graph ? open circle at origin?
Post by: joechan521 on October 31, 2007, 07:29:16 pm
when drawing a ray, something like arg(z)= pi/4
does the origin has to be drawn with an open circle???
since its not defined
Title: drawing Arg(z) graph ? open circle at origin?
Post by: Ahmad on October 31, 2007, 08:42:10 pm
Since arg(0) is undefined, it should be an open circle.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: joechan521 on November 01, 2007, 07:39:08 am
oh, my damn text book doesn't take that into account
Title: drawing Arg(z) graph ? open circle at origin?
Post by: Ahmad on November 01, 2007, 07:44:47 am
It may be right. Check what VCAA does to make sure.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: joechan521 on November 01, 2007, 07:54:34 am
how to check that? in study design? would they have such a minor thing?
Title: drawing Arg(z) graph ? open circle at origin?
Post by: enwiabe on November 01, 2007, 07:57:46 am
Check by logic!

z = x+yi

Arg(z) = tan^-1(y/x)

if x = 0 and y = 0 then you get tan^-1(0/0) which is clearly undefined.

Also, this was an issue on one of the exams from 2000-2002 that was covered in the assessment report. Not entirely sure which though.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: joechan521 on November 01, 2007, 08:07:11 am
my text book must be shit then
and it say its a new edition this yr, but theres more wrong answers than correct ones
Title: drawing Arg(z) graph ? open circle at origin?
Post by: Khangfu on November 01, 2007, 08:30:54 am
You should not test it like that. Just note that y/x, means x>0  or else Arg(z) is undefined.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: enwiabe on November 01, 2007, 08:32:33 am
That's... more or less the same thing?
Title: drawing Arg(z) graph ? open circle at origin?
Post by: brendan on November 01, 2007, 09:27:09 am
Quote from: "Ahmad"
It may be right. Check what VCAA does to make sure.


you don't need to. Arg(0+0i) is undefined
Title: drawing Arg(z) graph ? open circle at origin?
Post by: Khangfu on November 01, 2007, 09:28:50 am
in my view the difference is i accounted for everything and you used only (0,0) as an example. Which is all fine for this case butfor other things it might not work ... like proving for instance.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: Collin Li on November 01, 2007, 11:37:29 am
Commonsense dictates Arg(0) is undefined. What is the angle within the principal argument for 0+0i from a centre 0+0i?

Uhm, could be pi, could be 3pi/4, could be e... pick your favourite number in between (-pi, pi].

Therefore, it's not defined.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: boulos90 on November 03, 2007, 02:04:56 pm
Quote from: "enwiabe"
Check by logic!

z = x+yi

Arg(z) = tan^-1(y/x)

if x = 0 and y = 0 then you get tan^-1(0/0) which is clearly undefined.

Also, this was an issue on one of the exams from 2000-2002 that was covered in the assessment report. Not entirely sure which though.


Chuck norris can divide by zero :D
Title: drawing Arg(z) graph ? open circle at origin?
Post by: joechan521 on November 04, 2007, 11:05:25 am
we all know its undefined, i was asking whether we need to draw an open circle when graphing it.

probably should draw it to be safe
Title: drawing Arg(z) graph ? open circle at origin?
Post by: Collin Li on November 04, 2007, 11:42:31 am
Quote from: "joechan521"
we all know its undefined, i was asking whether we need to draw an open circle when graphing it.

probably should draw it to be safe


You must draw an open circle when graphing it. It will be checked.
Title: drawing Arg(z) graph ? open circle at origin?
Post by: joechan521 on November 04, 2007, 02:30:21 pm
Quote from: "coblin"
Quote from: "joechan521"
we all know its undefined, i was asking whether we need to draw an open circle when graphing it.

probably should draw it to be safe


You must draw an open circle when graphing it. It will be checked.

yeah thx, my stupid text book doesnt draw it, and my stupid teacher doesnt draw it either