sin（-1071°）×sin99°+sin（-171°）sin（-261°）
=sin（1080°-1071°）×sin(90°+9°)°+sin（360°-171°）sin（-261°+360°）
=sin9°*cos9°+sin(-9°)*cos9°
=sin9°*cos9°-sin9°*cos9°
=0