The sum of the degree and order of the following differential equation $$\left[1-\left(\frac{d y}{d x}\right)^2\right]^{\frac{3}{2}}=k x \frac{d^2 y}{d x^2}$$

The solution of the differential equation $${{{d^2}y} \over {d{x^2}}} = 0$$ represents

The solution of the differential equation $$\frac{d y}{d x}+\sqrt{\frac{1-y^2}{1-x^2}}=0$$ is

The solution of the differential equation $$x \frac{d y}{d x}=\cot y$$ is