LHS=tan A1+sec A−tan A1−sec A=tan A(1−sec A−1−sec A)(1+sec A)(1−sec A)
=tan A(−2 sec A)(1−sec2 A)=2 tan A.sec A(sec2 A−1) [∵(a+b)(a−b)=a2−b2]
=2 tan A.sec Atan2A [∵sec2A−tan2A=1]
[∵sec θ=1cos θ and tan θ=sin θcos θ]
=2 sec Atan A=2sin A=2 cosec A=RHS [∵cosec θ=1sin θ]