cos(θ+7π/2)=cos(θ+3π/2)tan(θ+3π/2)=sin(θ+3π/2)/cos(θ+3π/2)=√3 sin(θ+3π/2)=√3cos(θ+3π/2)sin²(θ+3π/2)+cos²(θ+3π/2)=1 -->cos²(θ+3π/2)=1/4显然θ+3π/2在一三象限 故cos(...