tolong bantu jawab soalnya penting utk uh! buktikan (sec a.cosec a-cot a) (sin a-cosec a)= -cos a?

( sec a . coseca - cot a ) ( sin a - cosec a ) = - cos a
( 1/sin a .1/cos a - cos a/sin a ) ( sin a - 1/sin a ) = - cos a
( 1/sinacosa - cos a/sina ) ( sin∧(2) a - 1/sin a ) = - cos a
( 1 - cos∧(2) a/sina cosa ) (sin a - 1 ) = - cos a
( 1 - cos a/ sian a ) ( - cos a ) = - cos a
( sin a/sin a ) ( - cos a ) = - cos a
( 1 ) ( - cos a ) = - cos a
- cos a = - cos a