I did it as the book says, but it doesn't work. Can someone help me??
This works fine for me:
Manipulate[Plot[soln /. {C[1] -> i, C[2] -> j}, {x, -2, 6}, PlotRange -> {-3, 3}], {i, -1, 1, 1}, {j, -1, 1, 1}, Initialization :> (soln = DSolveValue[y''[x] + y'[x] + y[x] == 0, y[x], x])]
Try typing it again in a new cell.
