Question

已知sin(π∕6+α)=1∕3，则cos（2π∕3-2α)的值等于

是π除以6的商再加上a

Answer 1

sin（π/6+a)=cos(1/2-π/6-a)=cos(π/3-a)=1/3
cos(2π/3-a)=2(cos(π/3-a))平方-1=2*(1/3)平方-1=-7/9
答案是-7/9
不懂用百度HI我