sin(-a-5π)cos(a-π/2)-tan(a-3π/2)tan(2π-a)
=sin(6π-a-5π)cos[-(π/2-a)]-tan(a-3π/2)tan(2π-a)
=sin(π-a)cos(π/2-a)+tan(2π+a-3π/2)tana
=sinasina+tan(π/2+a)tana
=(sina)^2-cotatana
=(sina)^2-1
=-cos^2a