Hi, I have got this differential equation:
y''=x*sin(y)
I am trying to use Mathematica 9 to solve this equation, so I write the following expression:
A = First[
y /. NDSolve[{y''[x] == x*Sin[y[x]], y[0] == 1, y'[0] == 1},
y, {x, 0, 19}]]
But Mathematica always answers with something like that:
"NDSolve::deqn: Equation or list of equations expected instead of True in the first argument {(y^[Prime][Prime])[x]==x Sin[y[x]],y[0]==1,True}. >>"
And
"ReplaceAll::reps: {NDSolve[{(y^[Prime][Prime])[x]==x Sin[y[x]],y[0]==1,True},y,{x,0,19}]} is neither a list of replacement rules nor a valid dispatch table, and so cannot be used for replacing. >>"
But a friend of mine has tried to input exactly what I wrote, and she got a normal result. She has Mathematica 10.
By answering a question, how many maximum and minimum has the function, the answer should be 8.
And my question is:
Is there any problem with Mathematica or can you see if I write something wrong?
Thanks to anyone who has tried solving this
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