thanYes, I forgot the x.When we differentiate, the term : sec^2ydy/dx must be multiplied by x ,and this term will be : xsec^2ydy/dx.
Thanks for correction.
This is the reply for bond girl007
Solution:
xtany=y-1
differentiate the two sides of the equation:
d/dx(xtany) =d/dx(y-1) Lows of differentiation
tany+sec^2(y)dy/dx=dy/dx
make dy/dx in one side: tany=(1-sec^2y)dy/dx
using laws of trigonometrics: tany=(-tan^2y)dy/dx...