Упростите выражение 1/8 cos4a+sin(^2) a*cos(^2)a-0,375

1/8cos²2a-1/8sin²2a+1/4sin²2a-0,375=
=1/8cos²2a+1/8sin²2a-0,375=
=1/8(cos²2a+sin²2a)-0,375=
=0,125*1-0,375=-0,25