LHS
= tan² x - 2 tan x cosec x + cosec² x - cot² x + 2 cot x sec x -
sec² x
= tan² x - 2 sec x + cosec² x - cot² x + 2 cosec x - sec² x
= ( tan² x - sec² x ) + (cosec² x - cot² x) + 2 cosec x - 2 sec
x
= -1 + 1 + 2 cosec x - 2 sec x
= 2 (cosec x - sec x)
= RHS (proved)
o.O
thx ^^
but y cannot use a^2 - b^2?