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Differentiate lnsecx

  • Thread starter thomas49th
  • Start date
  • #1
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Homework Statement


Given that y = lnsecx, - pi/2 <=x<=0, use the substituation u = secx, or otherwise, to show that dy/dx = tan x.

The Attempt at a Solution



well i thought about using the product rule, but you as it's ln(secx) not lnxsecx (2 different functions).... soooo im all out of ideas :(

Thanks :)
 

Answers and Replies

  • #2
32
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You could probably use chain rule...as in:

<< complete solution deleted by berkeman >>

Don't quote me on this, I'm still learning basic calculus.=D
 
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  • #3
Redbelly98
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You could probably use chain rule...
DMac,

FYI, it's preferable to just give hints, like the part I quoted above, rather than give complete solutions as you did.

Regards,

Mark
 
  • #4
tiny-tim
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Hi thomas49th! :smile:

The question says:
… use the substituation u = secx …
So try it … u = secx, so du = … ?, and y = … ? :smile:
 
  • #5
655
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chain rule:

dy/dx = dy/du . du/dx

dy/du of lnsecx = 1/secx

du/dx = secxtanx

1/secx . secxtanx = tanx

Cheers :)
 
  • #6
32
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Whoops sry guys, I'm still relatively new to the forum. My apologies.
 
  • #7
tiny-tim
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Whoops sry guys, I'm still relatively new to the forum. My apologies.
urrh …I was asleep! :zzz:

Listen for the snoring next time!
 
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