cos(π-θ)tan(3π+θ)/sin(π/2+θ)=3/4
(-cosθ)tanθ/cosθ=3/4
-tanθ=3/4
tanθ=-3/4
当θ为第二象限角时,cosθ=-4/5
当θ为第四象限角时,cosθ=4/5