已知cos(a-π/6)+sina=(4*根号3)/5,则sin(a-7π/6)的值是
问题描述:
已知cos(a-π/6)+sina=(4*根号3)/5,则sin(a-7π/6)的值是
答
cos(a-π/6)+sina=cosacosπ/6+sinasinπ/6+sina=cosa*(根号3)/2+sina*1/2+sina=cosa*(根号3)/2+sina*3/2=根号3*(cosa*1/2+sina*(根号3)/2=根号3*sin(π/6+a)=(4*根号3)/5所以sin(π/6+a)=4/5,cos(π/6+a)=±1...