Question

sin^4a-sin^2a*cos^2a-sin^2a

 

ctg(-a)*tg(-a)-sin^2(-a)

 

Answer 1

sin²a(sin²a-cos²a)-sin²a=sin²a(sin²a-cos²a-1)=sin²a(sin²a-cos²a-sin²a-cos²a)=
sin²a(-2cos²a)=-1/2sin²2a

-ctga*(-tga)-sin²a=1-sin²a=cos²a