x/5=cosψ y/3=sinψ => x^2/5^2=cos^2ψ y^2/3^2=sin^2ψ
=> x^2/5^2+y^2/3^2=c0s^2ψ+sin^2ψ=1
∴普通方程为 x^2/5^2+y^2/3^2=1 ,是一个长半轴为5,短半轴为3,焦点在x轴的椭圆.