tan周期是π
cos周期是2π
所以原式=tan(-a)cos(-a)sin(-a+3π/2-2π)/[cos(-a+π)sin(2π-π-a)]
=-tanacosasin(-a-π/2)/[-cosasin(π-a)]
=tanacosasin(a+π/2)/(-cosasina)
=(sina/cosa)cosacosa/(-cosasina)
=cosasina/(-cosasina)
=-1