Prove that Cot A -1 / 2- sec2 A = cot A/ 1+tan A
cot A-1 / 2-sec2A
= cot A-1 / 2-(1+tan2A)
= cot A-1 / 1-tan2A
= (1/tanA ) -1 / 1-tan2A [cotA =1/tanA]
=(1-tanA) /tanA / 1-tan2A [Taking LCM]
= (1-tanA) /tanA / (1+tanA)(1-tanA) [a2-b2 = (a+b)(a-b)]
=(1/tanA) / 1+tanA
= cotA / 1+tanA [1/tanA= cotA]
Proved