Question

高中数学两角和与差的正弦，余弦，正切公式

sin20cos110+cos160sin70
急求答案，谢谢！

Answer 1

sin20=cos70 cos110=-cos70 cos160=-cos20=-sin70
原式=-cos70cos70-sin70sin70=-(cos70cos70+sin70sin70)=-1
高考三角函数无非就是考变换、和差化积、积化和差、半角、2倍角公式加上一点函数的东西 运用熟练了很容易的
希望对你有用 谢谢！

Answer 2

cos110=cos(180-70)=-cos70
sin20=sin(90-20)=cos70

cos160=cos(180-20)=-cos20=-cos(90-70)=-sin70

故而原式=-(cos70cos70+sin70sin70)
=-1

Answer 3

sin20cos110+cos160sin70
=sin20cos110-cos(180-160)*sin(180-70)
=sin20cos110-cos20*sin110
=sin(20-110)
=sin(-90)=-1

Answer 4

sin20cos110+cos160sin70
=-sin20cos70-cos20sin70
=-(sin20cos70+sin70cos20)
=-sin(70+20)
=-sin90
=-1