tolong dong yang bisa matematika trigonometri

A. Cos (90-a )\sin (90-a ) = sin a/ cos a = tan a .
B. sec (90-a )\ cosec ( 180+a ) = cosec a\- cosec a = - 1
C. Sin (90-a )\ sin (90 + a )= cos a\ cos a = 1
D. Cos (180- a )\ sin (90- a ) = - cos a \ cos a
E. Cos ( 90 + a )\ cosec ( 180 - a ) = sin a \ cosec a