f(x) = cos x/(1 - sin x) - 1/cos x = [cos ^2 x - (1 - sin x)]/(cos x*(1 - sin x)f(x)=cosx1−sinx−1cosx=cos2x−(1−sinx)cosx⋅(1−sinx)
In the numerator of f(x),f(x), replace
cos^2 x = 1 - sin^2 xcos2x=1−sin2x
Numerator = 1 - sin^2 x - 1 + sin x ==1−sin2x−1+sinx=
sin x*(1 - sin x)sinx⋅(1−sinx)
f(x) = (sin x*(1 - sin x))/(cos x*(1 - sin x))= sin x/cos x = tan x.f(x)=sinx⋅(1−sinx)cosx⋅(1−sinx)=sinxcosx=tanx.