已知sinα=15/17 求cos﹙π/3+α﹚,cos﹙3/π-α﹚α属于﹙π/2,π﹚
问题描述:
已知sinα=15/17 求cos﹙π/3+α﹚,cos﹙3/π-α﹚
α属于﹙π/2,π﹚
答
两角差的余弦公式+诱导公式
答
cosa=-8/17cos﹙π/3+α﹚=cos(π/3)cosa-sin(π/3)sina=1/2×(-8/17)-√3/2×15/17=-4/17-15√3/34cos﹙3/π-α﹚=cos(π/3)cosa+sin(π/3)sina=1/2×(-8/17)+√3/2×15/17=-4/17+15√3/34...