sin(a+π/3)+sina= - 4根号3/5,则cos(a+2π/3)
问题描述:
sin(a+π/3)+sina= - 4根号3/5,则cos(a+2π/3)
怎么求》
答
sin(a+π/3)+sina
=1/2 sina+√3/2cosa+sina
=3/2sina+√3/2cosa
=√3(√3/2sina+1/2cosa)
=√3cos(a-π/3)
=-√3cos(a+2π/3)
然后用已知的带一下就行了 ..