You are Here: Home

# Differentiating Tan Tweet

Maths and statistics discussion, revision, exam and homework help.

Announcements Posted on
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
1. Differentiating Tan
x=tan(3y+1)

What would be dx/dy?

Cheers
2. Re: Differentiating Tan
(Original post by LimeTree.)
x=tan(3y+1)

What would be dx/dy?

Cheers
3sec^2(3y+1)
using differentiation by substitution
3. Re: Differentiating Tan
d(tan x)/dx = (sec x)^2

Try using the substitution u = 3y+1
4. Re: Differentiating Tan
Thankyou!

How do I use the substitution?

Sorry, I just really dont understand this
5. Re: Differentiating Tan
(Original post by LimeTree.)
Thankyou!

How do I use the substitution?

Sorry, I just really dont understand this
if x=tanu
dx/du=sec^2u
dx/dy=dx/du x du/dx
u=ax
du/dx=a
dx/dy=asec^2 ax
6. Re: Differentiating Tan
(Original post by roar558)
if x=tanu
dx/du=sec^2u
dx/dy=dx/du x du/dx
u=ax
du/dx=a
dx/dy=asec^2 ax
Thankyou very much!

So x=tan(4y+2)
x=tanu
dx/du=sec^2u

u=4y+2
du/dx=4

dx/dy *du/dx = 4Sec^2(4y+2)

So use chain rule with substitution?

Thanks
7. Re: Differentiating Tan
Another way to think about it is to use the identity that and then to use quotient rule so in your case:

So that's always an option if you don't want to use substitution
8. Re: Differentiating Tan
(Original post by LimeTree.)
Thankyou very much!

So x=tan(4y+2)
x=tanu
dx/du=sec^2u

u=4y+2
du/dx=4

dx/dy *du/dx = 4Sec^2(4y+2)

So use chain rule with substitution?

Thanks
Yep essentially, np