=(sin²θ+cos²θ)/(-sin²θ+4sinθcosθ-3cos²θ）
=(tan²θ+1)/(-tan²θ+4tanθ-3) 分子分母同时除以cos²θ
=(16/9+1)/(-16/9-16/3-3)
=25/(-16-48-27)
=-25/93