1tan3A−tanA−1cot3A−cotA=
cot2A
1tan3A−tanA−1cot3A−cotA
Substituting cot3A = 1tan3A & cotA = 1tanA
= 1tan3A−tanA−11tan3A−1tanA
= 1tan3A−tanA−tanA.tan3AtanA−tan3A
= 1tan3A−tanA+tanA.tan3Atan3A−tanA
= (1+tanA.tan3A)tan3A−tanA
= 1tan(3A−A)
= cot2A
= cot2A−12cotA
Options B & D are correct.