(a)

> MODEL := diff( x(t), t ) = t/x(t);

> SOLN := dsolve( MODEL, x(t) );

> solve( SOLN, { x(t) } );

Error, (in solve) invalid arguments

Note that the full solutions can be either the positive or negative branch of the square root (depending on the sign of the initial condition). Also, the initial condition cannot be of the form .

>