How do I start to differentiate this? Watch

username970964
Badges: 14
Rep:
?
#1
Report Thread starter 4 years ago
#1
Name:  20150517_185240.jpg
Views: 1026
Size:  457.4 KB

Multiply out the bracket (put sin on both lines)? Or leave it as it is? I know I then have to use the quotient rule.
0
reply
MathsNerd1
  • Study Helper
Badges: 17
Rep:
?
#2
Report 4 years ago
#2
(Original post by Airess3)


Multiply out the bracket (put sin on both lines)? Or leave it as it is? I know I then have to use the quotient rule.
If you do the chain rule and quotient rule as you would normally then that should get you the right answer
0
reply
Hasufel
Badges: 16
Rep:
?
#3
Report 4 years ago
#3
(Original post by MathsNerd1)
If you do the chain rule and quotient rule as you would normally then that should get you the right answer
note that, simplified, what you have inside the brackets is:

\displaystyle 1- \frac{2}{1+e^{2x}}

i.e. , you`d then have : \displaystyle \sin(A-B) = \sin(1) \cos( \frac{2}{1+e^{2x}})- \cos(1) \sin( \frac{2}{1+e^{2x}})

which is somewhat (i think) easier to differentiate....

EDITED
0
reply
username970964
Badges: 14
Rep:
?
#4
Report Thread starter 4 years ago
#4
(Original post by Hasufel)
note that, simplified, what you have inside the brackets is:

\displaystyle 1+ \frac{2}{1+e^{2x}}

i.e. , yopu`d have inside: \displaystyle \sin(A+B) = \sin(1) \cos( \frac{2}{1+e^{2x}})+ \cos(1) \sin( \frac{2}{1+e^{2x}})

which is somewhat (i think) easier to differentiate....
Where does the 1 come from beside the sin and cos?
1
reply
Jai Sandhu
Badges: 12
Rep:
?
#5
Report 4 years ago
#5
(Original post by Airess3)


Multiply out the bracket (put sin on both lines)? Or leave it as it is? I know I then have to use the quotient rule.
This is undergraduate o.O please tell me it is part of some insane thing I do not understand.
0
reply
Hasufel
Badges: 16
Rep:
?
#6
Report 4 years ago
#6
(Original post by Airess3)
Where does the 1 come from beside the sin and cos?
beg your pardon - the sign between is a minus!!

from the rule above:  \sin( 1- \frac{2}{1+e^{2x}}) \equiv  \sin(1) \cos( \frac{2}{1+e^{2x}})- \cos(1) \sin(\frac{2}{1+e^{2x}})
0
reply
username970964
Badges: 14
Rep:
?
#7
Report Thread starter 4 years ago
#7
(Original post by Jai Sandhu)
This is undergraduate o.O please tell me it is part of some insane thing I do not understand.
It is first year university level (first semester work).
0
reply
Smaug123
  • Study Helper
Badges: 13
Rep:
?
#8
Report 4 years ago
#8
(Original post by Airess3)


Multiply out the bracket (put sin on both lines)? Or leave it as it is? I know I then have to use the quotient rule.
I'm scared by your phrase "put sin on both lines". It's not true that \sin(\frac{a}{b}) = \frac{\sin(a)}{\sin(b)}.
1
reply
Smaug123
  • Study Helper
Badges: 13
Rep:
?
#9
Report 4 years ago
#9
(Original post by MathsNerd1)
If you do the chain rule and quotient rule as you would normally then that should get you the right answer
It might help, by the way, to know that g(x) = \sin(\text{tanh}(x)). That's immediately amenable to the chain rule if you know \text{tanh}'.
1
reply
lizard54142
Badges: 6
Rep:
?
#10
Report 4 years ago
#10
(Original post by Airess3)
Name:  20150517_185240.jpg
Views: 1026
Size:  457.4 KB

Multiply out the bracket (put sin on both lines)? Or leave it as it is? I know I then have to use the quotient rule.
(Original post by Smaug123)
I'm scared by your phrase "put sin on both lines". It's not true that \sin(\frac{a}{b}) = \frac{\sin(a)}{\sin(b)}.
In the nicest possible way, why are you studying maths at university if you think this?
0
reply
Smaug123
  • Study Helper
Badges: 13
Rep:
?
#11
Report 4 years ago
#11
(Original post by lizard54142)
In the nicest possible way, why are you studying maths at university if you think this?
Brain farts are a thing - I've asserted in the past that it wasn't blindingly obvious that there are arbitrarily large finite groups :P
0
reply
username970964
Badges: 14
Rep:
?
#12
Report Thread starter 4 years ago
#12
(Original post by Hasufel)
from the rule above:  \sin( 1+ \frac{2}{1+e^{2x}}) \equiv  \sin(1) \cos( \frac{2}{1+e^{2x}})+ \cos(1) \sin(\frac{2}{1+e^{2x}})
So that's the answer an the question is finished?
0
reply
Hasufel
Badges: 16
Rep:
?
#13
Report 4 years ago
#13
(Original post by Smaug123)
It might help, by the way, to know that g(x) = \sin(\text{tanh}(x)). That's immediately amenable to the chain rule if you know \text{tanh}'.
b****g me! - didn`t see that!
0
reply
username970964
Badges: 14
Rep:
?
#14
Report Thread starter 4 years ago
#14
(Original post by lizard54142)
In the nicest possible way, why are you studying maths at university if you think this?
Maths isn't my degree, I'm just doing a side course in it.
1
reply
rayquaza17
Badges: 17
Rep:
?
#15
Report 4 years ago
#15
(Original post by lizard54142)
In the nicest possible way, why are you studying maths at university if you think this?
There isn't a nice way to say that at all.
Everyone makes mistakes.
1
reply
Smaug123
  • Study Helper
Badges: 13
Rep:
?
#16
Report 4 years ago
#16
(Original post by Hasufel)
b****g me! - didn`t see that!
Now I'm consumed with curiosity as to what the asterisked word is.
2
reply
username970964
Badges: 14
Rep:
?
#17
Report Thread starter 4 years ago
#17
(Original post by Hasufel)
beg your pardon - the sign between is a minus!!

from the rule above:  \sin( 1- \frac{2}{1+e^{2x}}) \equiv  \sin(1) \cos( \frac{2}{1+e^{2x}})- \cos(1) \sin(\frac{2}{1+e^{2x}})
What do I do now?
0
reply
Hasufel
Badges: 16
Rep:
?
#18
Report 4 years ago
#18
(Original post by Smaug123)
Now I'm consumed with curiosity as to what the asterisked word is.
ha! - lol - just realised i meant to type something that rhymed with "bug her" said quickly!!
0
reply
Hasufel
Badges: 16
Rep:
?
#19
Report 4 years ago
#19
Airees3 - ignore my post - follow smaug123`s tip - that`s a damn sight easier than mine! (my lack of insight has led me astray here, and i need a spanking, nurse....)
2
reply
rayquaza17
Badges: 17
Rep:
?
#20
Report 4 years ago
#20
(Original post by Hasufel)
my lack of insight has led me astray here, and i need a spanking, nurse....)
:eek:
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Warwick
    Warwick Business School Postgraduate
    Thu, 20 Feb '20
  • St George's, University of London
    Postgrad open day Postgraduate
    Thu, 20 Feb '20
  • University of Hertfordshire
    All Subjects Undergraduate
    Sat, 22 Feb '20

People at uni: do initiations (like heavy drinking) put you off joining sports societies?

Yes (228)
67.66%
No (109)
32.34%

Watched Threads

View All