已知cos(a-π/6)+sina=4根号下3/5,则sin(a+7π/6)=?
问题描述:
已知cos(a-π/6)+sina=4根号下3/5,则sin(a+7π/6)=?
答
根据:cos(a-π/6)+sina=(4*根号3)/5有:cosacosπ/6+sinasinπ/6+sina=(4*根号3)/5(根号3)/2cosa+3/2sina=(4*根号3)/5得到:cosa+(根号3)sina=8/5所以:sin(a+7π/6)=sinacos7π/6+cosasin7π/6=(-根号3)/2si...