ATAR Notes: Forum

VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: Fitness on November 07, 2007, 08:15:23 pm

Title: I can't see how this works . . .
Post by: Fitness on November 07, 2007, 08:15:23 pm

Ok there is this question in the itute 2006 trial exam 1. I can do part A and B ok. But I am stumped on why itute's answer is what it is for part C. It could be something obvious but I need to know what's going on with it.

(http://i180.photobucket.com/albums/x69/gourlaype/lolwtfidk.jpg)

Part A and B are easy. But for part C I put domain: R
Itute's answer is:
(http://i180.photobucket.com/albums/x69/gourlaype/lolwtfidkanswer.jpg)

Can anyone tell me why it's \{1}? I don't see why that isn't part of the domain... Why isn't x=1 differentiable? :?

Title: I can't see how this works . . .
Post by: joechan521 on November 07, 2007, 08:20:54 pm

for that graph, y=|x^3-1|
theres a sharp turn, at where it meets the x-axis, the point(1,0)
its the pointy thing, you can see it from your graph.
at that point, you cannot find the gradient of it
hence dy/dx is not defined at x=1

Title: I can't see how this works . . .
Post by: Fitness on November 07, 2007, 08:24:15 pm

Quote from: "joechan521"

for that graph, y=|x^3-1|
theres a sharp turn, at where it meets the x-axis, the point(1,0)
its the pointy thing, you can see it from your graph.
at that point, you cannot find the gradient of it
hence dy/dx is not defined at x=1

Argh! I knew it was something simple!

Thanks heaps joechan521 :D

Title: I can't see how this works . . .
Post by: melanie.dee on November 07, 2007, 08:24:20 pm

ah yeh i did a question like this and i was totally like wtf why, but yeh tis cos of the pointy join. whatever they're called. cusp?

Title: I can't see how this works . . .
Post by: Fitness on November 07, 2007, 08:26:55 pm

Quote from: "melanie.dee"

ah yeh i did a question like this and i was totally like wtf why, but yeh tis cos of the pointy join. whatever they're called. cusp?

Yes a cusp. The funny thing is I leaned something about this and totally forgot!  :wink: