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Mathematics 9 Online
OpenStudy (dls):

DE~!

OpenStudy (dls):

\[y=\tan^{-1} \sqrt{\frac{1-cosx}{1+cosx}} \]

OpenStudy (dls):

I tried to solve till some extent

OpenStudy (anonymous):

well, you might notice that if the part behind there look very very similar to \(\tan \theta\) if you've done some rearranging.

OpenStudy (sirm3d):

and the answer is \[\large \frac{ dy }{ dx }=\frac{ 1 }{ 2 }\]right?

hartnn (hartnn):

try to get y=x/2.

OpenStudy (dls):

\[\frac{dy}{dx}=\frac{1}{1+\frac{1-cosx}{1+cosx}} \times \frac{1}{2 \sqrt{\frac{1+cosx}{1-cosx}}} \times 1+\cos x d(\frac{1-cosx}{(1+cosx)^{2}}) - (1-cosx) d \frac{1+cosx}{(1+cosx) ^{2}} \]

OpenStudy (dls):

wth :o

OpenStudy (anonymous):

use the half angle formulas to reduce \(\sqrt \frac{1- \cos x}{1+\cos x}\) into \(\tan \frac{x}{2}\), then start differentiating.

hartnn (hartnn):

use 1-cos 2theta =... ? 1-sin 2theta=.....? in terms of theta.

hartnn (hartnn):

*1+cos 2theta=...

OpenStudy (dls):

2cos^2 theta

OpenStudy (dls):

where do i have to use it but?

hartnn (hartnn):

so, 1+cos x = 2cos^2 x right ?

hartnn (hartnn):

*1+cos x = 2cos^2 (x/2)

OpenStudy (dls):

yeah! u confused me for a second :P

hartnn (hartnn):

ans 1-cos x = ?

OpenStudy (dls):

-2cos(x/2)?

hartnn (hartnn):

no!

OpenStudy (dls):

:O

hartnn (hartnn):

1-cos 2theta = 2 sin^2 theta

OpenStudy (dls):

yes

hartnn (hartnn):

so, 1-cos x = ?

OpenStudy (dls):

2sin sq theta/2

hartnn (hartnn):

2sin^2 x/2 now put this in your y=...

hartnn (hartnn):

what u get ?

OpenStudy (dls):

2cos ^ theta/2sin ^ theta

OpenStudy (sirm3d):

2 theta on the LHS of the identity, theta on the RHS of the identity x on the LHS, what do you think is the RHS?

OpenStudy (dls):

thatis powerr 2*

hartnn (hartnn):

yeah, and theres square root, so that simplifies to ?

OpenStudy (dls):

cos/sin

OpenStudy (dls):

tan theta :o

hartnn (hartnn):

sin/cos = tan (x/2)

OpenStudy (dls):

yes

hartnn (hartnn):

so y=... ?

OpenStudy (dls):

tan inverse tan x/2

OpenStudy (dls):

\[\frac{1}{1+\frac{\tan^{2}x}{4}} \]?

hartnn (hartnn):

\(\tan^{-1}(tan \theta) = \theta\)

OpenStudy (sirm3d):

tan^{-1} is supposed to "cancel" the tan, basic concept of an inverse function.

hartnn (hartnn):

\(\tan^{-1}(tan \: x/2) = x/2\)

OpenStudy (dls):

oh.! okay...thanks :D

OpenStudy (dls):

Arigato senseis'!

hartnn (hartnn):

whats that ?

OpenStudy (dls):

Thank you,teacher(s) <3

OpenStudy (dls):

japanese phrase :P

hartnn (hartnn):

ohh! welcome ^_^

OpenStudy (sirm3d):

sensei = teacher hahaha

OpenStudy (dls):

yeah ! :D

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