Find the st values and determine each stationary value (min or max)
y=e^-x(sinx)
When i differentiate I get -e^-x = 0.
What do I do when I get to this stage??
Thanks
0
HELP PLEASE stationary values
Started by AM4R, Nov 08 2006 08:04 PM
8 replies to this topic
#1
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Posted 08 November 2006 - 08:04 PM
Can someone please please try and help me with this question thanks.
Find the st values and determine each stationary value (min or max)
y=e^-x(sinx)
When i differentiate I get -e^-x = 0.
What do I do when I get to this stage??
Thanks
Find the st values and determine each stationary value (min or max)
y=e^-x(sinx)
When i differentiate I get -e^-x = 0.
What do I do when I get to this stage??
Thanks
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#2
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Posted 08 November 2006 - 08:20 PM
Use logs of base e on both sides and u'll end up with x= log of base e to the 0. I think!
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#3
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Posted 08 November 2006 - 08:30 PM
Thanks for the help but how do I do that?
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#4
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Posted 08 November 2006 - 09:03 PM
That's a good question! You can't - think about the graph of 
, this is never zero.
You've not differentiated correctly, I get
.
Does this help?
, this is never zero.You've not differentiated correctly, I get
.Does this help?
#5
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Posted 08 November 2006 - 09:57 PM
yup your right, but where do I go from there? and how do I factorise it?
Thanks
Thanks
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#6
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Posted 09 November 2006 - 11:17 AM
Ah yes he's right. You must now use logs of base e. So you get log to the base e of e to the power of -x, this simply becomes -x since log of e to the e is 1. So you have -x times (cos x- sinx) which becomes -xcosx+xsinx. I'm sure you (using the standard formulas given in past papers and textbooks etc)can rearrange this to form the answer.
P.S I may be wrong, maybe its best to PM Dave, he's the maths wizard! Maths isn't exactly my forte!
P.S I may be wrong, maybe its best to PM Dave, he's the maths wizard! Maths isn't exactly my forte!
Half ideas,half quality, half a million pound law suit!
#7
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Posted 09 November 2006 - 07:36 PM
Sorry Discogirl, but that's completely wrong!
We want to solve
So, just in the usual way,
or 
. The first equation has no solutions, but it remains to find solutions to the second one, i.e. 
.
This is something you'll have done at Higher.
We want to solve
So, just in the usual way,
or . The first equation has no solutions, but it remains to find solutions to the second one, i.e. .This is something you'll have done at Higher.
#8
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Posted 11 November 2006 - 10:30 PM
Like I said, maths isnt my forte lol!
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#9
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Posted 11 November 2006 - 11:10 PM
QUOTE(Discogirl17 @ Nov 9 2006, 11:17 AM) 
P.S I may be wrong, maybe its best to PM Dave, he's the maths wizard! Maths isn't exactly my forte!
lol i have her well trained
If i am not here i am somewhere else
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