Question

已知cosa=3/5,且a属于(3pi/2,2pi),则cos(a-pi/3)=

Answer 1

已知,cosa = 3/5 ,且a 属于 (3π/2,2π) 在第四象限,

则有：sina = -√(1-cos²a) = -4/5 ；

可得：cos(a-π/3) = cosa*coa(π/3)+sina*sin(π/3) = (3/5)*(1/2)+(-4/5)*(√3/2) = (3-4√3)/10 .