cos(-585°)/sin630°+sin( -690°)
问题描述：
cos(-585°)/sin630°+sin( -690°)
答
cos(-585°)/sin630°+sin( -690°)=cos(720°-585°)/sin(720°-90°)+sin(720° -690°)=cos135°/(-sin90°)+sin30°=cos(180°-45°)/(-sin90°)+sin30°=-cos45°/(-sin90°)+sin30°=cos45°/sin90°+sin30°=...