| FragKrag United States. October 01 2008 13:07. Posts 11068 | Profile Blog # |
hihi T_T
New Problem:X^3+Y^3=125
dy/dx =?
a. -x/y
b.-x/5y
c. y/x
d. x/(y-5)
e. x/y
Well, I thought it was -(x/y)^2, but it's not on there.
I think that it should be negative, and there should not be a 5, which leaves me -x/y, which is x^2+y^2=C
Problem: The function y=|x-8|+2 is differentiable over..
a. [8,10)
b. (2,10)
c. [2,10]
d. [2,10)
e. (2,10]
halps would be appreciated <3
Edit: What we got is that since [8,10) has a continuous slope of 1, it's right.Last edit: 2008-10-22 12:28:28
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| | *TL CJ Entusman #40* "like scissors does anything to paper except MAKE IT MORE NUMEROUS" -paper | |
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| Saracen United States. October 01 2008 13:11. Posts 5127 | Profile Blog # |
graph it
if the sharp point from the absolute value is included in your set of points, then no
if not, then yes |
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| doghunter United States. October 01 2008 13:13. Posts 23 | Profile Blog # |
| It's not differentiable at x=8 (cusp), so I thought the answer would be (-inf,8),(8,inf) but that doesn't seem to be an answer. |
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| Avidkeystamper United States. October 01 2008 13:13. Posts 8551 | Profile Blog # |
| It's a, all the other intervals include the corner of the V the graph produces and that corner is not differentiable since the slope from both sides is not the same. Notice how a does not include 8 in its interval since that point is part of the corner and is not differentiable (<-I think?) |
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| FragKrag United States. October 01 2008 13:18. Posts 11068 | Profile Blog # |
We did graph it, and it's a V, but 2,10 all contain two slopes, 1 and -1 as derivatives.
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| | *TL CJ Entusman #40* "like scissors does anything to paper except MAKE IT MORE NUMEROUS" -paper | |
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| doghunter United States. October 01 2008 13:32. Posts 23 | Profile Blog # |
| There's no limit from the left side, so you can't say that there is a limit at x=8 |
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| vAltyR United States. October 01 2008 13:36. Posts 580 | Profile Blog # |
what it's asking is if you get a continuous derivative over the intervals. If I'm interpreting the equation right, the point of the "V" should be at x=8, therefore the derivative at x=8 does not exist, eliminating all the intervals between 2 and 10, whether or not they actually *include* 2 or 10. the answer is a.
man, that's a *precalc* question? we never covered that until calculus. in fact, i never even heard the word "derivative" until i opened a calc book. |
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| thunk United States. October 01 2008 13:48. Posts 6233 | Profile Blog # |
8 is a point of non-differentiability, so I think that (a) is also wrong. But for sure b-e are wrong more so, so it's definitely A.
On October 01 2008 13:32 doghunter wrote:
There's no limit from the left side, so you can't say that there is a limit at x=8
It's continuous and the limit as x approaches 8 exists. It's just no differentiable because the derivative from the right and the derivative from the left are inequal. Last edit: 2008-10-01 13:50:28 |
| | Every time Jung Myung Hoon builds a vulture, two probes die. || My post count was a palindrome and I was never posting again. |
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| Purind Canada. October 01 2008 23:56. Posts 3373 | Profile Blog # |
| See I thought a would be wrong too, but if you only graph that interval, you get a straight line and you don't see the pointiness |
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| SIUnit China. October 02 2008 01:29. Posts 288 | Profile # |
| Asia tend to be a bit crazy on the math side of things. And yeah, this would technically be a calc 1 question here in the states. |
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| FragKrag United States. October 22 2008 12:28. Posts 11068 | Profile Blog # | |
| | *TL CJ Entusman #40* "like scissors does anything to paper except MAKE IT MORE NUMEROUS" -paper | |
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| skyglow1 New Zealand. October 22 2008 13:46. Posts 3961 | Profile Blog # |
Use implicit differentiation which involves chain rule.
x^3+y^3=125
Differentiation both sides by x: 3x^2+d(y^3)/dx=0
Since y is a function of x, and using chain rule: d(y^3)/dx = 3y^2 x dy/dx
So you get: 3x^2 + 3y^2 x dy/dx = 0
And rearranging: dy/dx = -3x^2/3y^2
[Edit] I'm a retard -_-Last edit: 2008-10-23 00:40:28 |
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| SaveYourSavior United States. October 22 2008 17:18. Posts 1071 | Profile Blog # |
what i got was -x^2 / y^2
but
a seems to be the right answer since it seems the most right |
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 Divinek Canada. October 22 2008 17:30. Posts 4016 | Profile Blog # |
On October 22 2008 13:46 skyglow1 wrote:
Use implicit differentiation which involves chain rule.
x^3+y^3=125
Differentiation both sides by x: 3x^2+d(y^3)/dx=0
Since y is a function of x, and using chain rule: d(y^3)/dx = 3y^2 x dy/dx
So you get: 3x^2 + 3y^2 x dy/dx = 0
And rearranging: dy/dx = -3x^2/3y^2 = -x/y so the answer should be a)
Implicit differentiation is in pre calc?
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| Never attribute to malice that which can be adequately explained by stupidity.
Oh goodness me, FOX tv where do you get your sight? Can't you keep track, the puck is black. That's why the ice is white. |
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| Ecael United States. October 22 2008 18:10. Posts 4902 | Profile # |
On October 22 2008 17:30 Divinek wrote:
Show nested quote +On October 22 2008 13:46 skyglow1 wrote:
Use implicit differentiation which involves chain rule.
x^3+y^3=125
Differentiation both sides by x: 3x^2+d(y^3)/dx=0
Since y is a function of x, and using chain rule: d(y^3)/dx = 3y^2 x dy/dx
So you get: 3x^2 + 3y^2 x dy/dx = 0
And rearranging: dy/dx = -3x^2/3y^2 = -x/y so the answer should be a)
Implicit differentiation is in pre calc?
If memory serves schools in Taiwan covered power rule to implicit differentiation in precalc, at least that's what I recall of what my friends/parents/family's talks of how they had it tough 
EDIT - It'd be hilarious when OP posts to say how he isn't at Taiwan though.  Last edit: 2008-10-22 18:11:32 |
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| FragKrag United States. October 22 2008 23:56. Posts 11068 | Profile Blog # |
I thought it was a nationality? T__________T
I'm taking "PreCalculus". It's the course name, but the book has PreCalc and Calc I so lol tt;;
anyways, how can you go from -(x/y)^2 to -x/y? ?:/
Last edit: 2008-10-22 23:59:35 |
| | *TL CJ Entusman #40* "like scissors does anything to paper except MAKE IT MORE NUMEROUS" -paper | |
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| skyglow1 New Zealand. October 23 2008 00:41. Posts 3961 | Profile Blog # |
| Sorry I'm so retarded. I shouldn't try to help at math when I don't learn it anymore |
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| FragKrag United States. October 23 2008 09:49. Posts 11068 | Profile Blog # |
;_________;
Today my math teacher tells me that "abcde" is a choice when you cant find the answer. --;Last edit: 2008-10-23 09:50:08 |
| | *TL CJ Entusman #40* "like scissors does anything to paper except MAKE IT MORE NUMEROUS" -paper | |
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| onihunter United States. October 23 2008 10:23. Posts 490 | Profile Blog # |
On October 23 2008 09:49 FragKrag wrote:
;_________;
Today my math teacher tells me that "abcde" is a choice when you cant find the answer. --;
Nice, would explain a lot about why I couldn't figure this problem out lol. And man I hate it when math questions have "None of the above" as a choice. |
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| Ecael United States. October 23 2008 11:40. Posts 4902 | Profile # |
On October 23 2008 09:49 FragKrag wrote:
;_________;
Today my math teacher tells me that "abcde" is a choice when you cant find the answer. --;
Ah good, I was going a bit insane and trying to log this through to solve earlier. |
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