質問: x acos(2πft + α)
回答: x = acos(2πft+α) y = bsin(2πft + α) x/a = cos(2πft+α) y/b =sin(2πft + α) (x/a)^2+(y/b)^2=[ cos(2πft+α)]^2+[sin(2πft + α)]=1