why do i get this 

"Error, (in solve) cannot solve expressions with diff(diff(y(x), x), x) for x"

when i input these: 

> restart; with(DEtools); with(plots); with(linalg);
> ode2 := x^2*(diff(y(x), `$`(x, 2)))+x*(diff(y(x), x))+4*y(x) = -2*x+7; bc2 := y(1) = 7, y(4) = -1;

a := 1; b := 4

ic2 := bc2[1], (D(y))(a) = alpha

constraint := lhs(bc2[2])-rhs(bc2[2]); constraint = 0

Hi,i'm new with maple, please help me solve these 2nd order ODES :)

x''=-x/((x^2+y^2)^(3/2))

y''=-y/((x^2+y^2)^(3/2))

my codes are:

declare((x, y)*t)

deq2 := diff(x(t), `$`(t, 2)) = -x(t)/(x(t)^2+y(t)^2)^(3/2), diff(y(t), `$`(t, 2)) = -y(t)/(x(t)^2+y(t)^2)^(3/2)

ic2 := x(0) = 1, (D(x))(0) = 0, y(0) = 0, D(y) = 1

rosen := dsolve({ic2, deq2}, type = numeric, stiff = true, {x(t), y(t)})