利用和(差)角公式求下列各三角函数的值(1)cos 17π/12 (2)sin(-61π/12)
问题描述:
利用和(差)角公式求下列各三角函数的值(1)cos 17π/12 (2)sin(-61π/12)
答
(1)cos 17π/12 =cos(π+5π/12)=-cos5π/12=-sinπ/12=-sin15度=-sin(45-30)=-根号2/4+根号6/4
(2)sin(-61π/12)=sin(-6π+11π/12)=sin11π/12=sin(π-π/12)=sinπ/12=-上式