Hi there!
L.H.S. = [tex] \dfrac{cos \: x}{cos \: x - sin \: x} [/tex]
Divide th' whole expression by cos x :-
[tex] \dfrac{ \dfrac{cos \: x}{cos \: x} }{ \dfrac{cos \: x}{cos \: x} \: - \: \dfrac{sin \: x}{cos \: x} } [/tex]
[tex] \dfrac{1}{1 - tan \: x} [/tex] = R.H.S.
HENCE PROVED.
~ Hope it helps!
