The Student Room Group
Reply 1
I think you mean

dy/dx = cos^2y / ( 2tany + 1)

If you weren't looking at it like this then you should now be able to do it fairly easily.
Reply 2
no i kno wat i wrote.
it was correct
if u cant help, then its kool
but can some one help me with the original equation
Reply 3
ash213
given that

x = sec^2 y + tan y

show that

dy/dx = cos^2 y / 2tan y + 1


thank you, who ever does this, i really appreciate your help
its a hard question, so could you set it out in easy steps. thanks again!


differentiate sec²y by chain rule
x=sec²y let sec y = t so that dt/dy = secy.tany
x= so dx/dt = 2t
dx/dy = dx/dt x dt/dy = 2t.secy.tany = 2 sec²y.tany

include +tany
dx/dy = 2 sec²y.tany + sec²y = sec²y(2tany+1) = (2tany+1) /cos²y
Invert.

Aitch
Reply 4
no i kno wat i wrote.
it was correct
if u cant help, then its kool
but can some one help me with the original equation
Reply 5
ash213
no i kno wat i wrote.
it was correct
if u cant help, then its kool
but can some one help me with the original equation


See solution above!
Reply 6
Isnt dx/dy cos^2 y / (2tan y + 1) and not dy/dx...?
Reply 7
Vazzyb
Isnt dx/dy cos^2 y / (2tan y + 1) and not dy/dx...?


The last line of my working has to be inverted to get q.e.d.

Aitch