Problem with Plot?

Questions
1

I did it as the book says, but it doesn’t work. Can someone help me??

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23.png993×881 44.2 KB

12.png
12.png1435×304 83.8 KB

2

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.