Question

已知向量a=(tana,1),b=(根号3,-1),a∈(π,2π)且a‖b,则点P(cos (π/2+a),sin（π

Answer 1

由a‖b得 (tana)(-1)-(1)(根号3)=0

解得tana= - 根号3,因a∈(π,2π) 故a=5π/3

cos (π/2+a)=-sina=-sin5π/3=sin(2π/3)=(根号3)/2>0

sin（π-a）=sin(π-5π/3)=sin(-2π/3)= - (根号3)/2