sin(5π/4)/cos(9π/4+a)xcos(7π/4-a)=sin(π+π/4)/cos(2π+π/4+a)xcos(2π-π/4-a)=sin(π+π/4)/cos(2π+π/4+a)xcos(2π-π/4-a)=-sinπ/4/cos(π/4+a)xcos[2π-(π/4+a)]=-sinπ/4/cos(π/4+a)xcos(π/4+a)=-...