What is the solution of the differential equation $$\ln \left( {{{dy} \over {dx}}} \right) - a = 0$$ ?

The differential equation of the family of curves $$y = p\cos (ax) + q\sin (ax)$$, where p, q are arbitrary constants, is

The equation of the curve passing through the point ($$-$$1, $$-$$2), which satisfies $${{dy} \over {dx}} = - {x^2} - {1 \over {{x^3}}}$$ is

What is the order of the differential equation whose solution is $$y = a\cos x + b\sin x + c{e^{ - x}} + d$$, where a, b, c and d are arbitrary constants?