Author 
Comment/Response 
yehuda

02/23/13 6:45pm
It seems that in one of your previous trials you set a value to y'[0] which was different than 1/3 and since it has a value Mathematica is able to evaluate y'[0]==1/3 and conclude it is wrong
Here is an example.
DSolve[{y''[x] + 2 y'[x] + y[x] == Sin[x], y'[0] == 0, y[0] == 1},
y[x], x]
returning
{{y[x] > (1/2) E^x (3  3 x + E^x Cos[x])}}
now
y'[0] = 5
and try again the previous call to NDSolve
DSolve[{y''[x] + 2 y'[x] + y[x] == Sin[x], y'[0] == 0, y[0] == 1},
y[x], x]
returning
DSolve[{y[x] + 2 Derivative[1][y][x] + (y^\[Prime]\[Prime])[x] ==
Sin[x], False, y[0] == 1}, y[x], x]
yehuda
URL: , 
