cos2a/sin（a-π/4)= -√2/2,sin(π/2-2a) /sin（a-π/4)= -√2/2,-sin(2a-π/2) /sin（a-π/4)= -√2/2,[-2 sin（a-π/4)cos（a-π/4)） /sin（a-π/4)= -√2/2,-2 cos（a-π/4)）= -√2/2,-2[cos a cosπ/4+sin a ...