已知cosa=4/5,a∈(-π/2,0),求tan2a的值 求sin(a-π/3)的值
问题描述:
已知cosa=4/5,a∈(-π/2,0),求tan2a的值 求sin(a-π/3)的值
答
sina=-3/5
tan2a=2sinacosa/(2cos²a-1)= -24/7
sin(a-π/3)=sinacosπ/3 -cosasinπ/3=(-3/5)*(1/2)-(4/5)*(√3/2)= - 3/10 - 2√3 /5