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A199429
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Decimal expansion of x>0 satisfying x^2+x*sin(x)=cos(x).
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57
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6, 4, 3, 4, 3, 6, 3, 6, 4, 1, 3, 8, 0, 2, 6, 1, 5, 8, 6, 4, 2, 0, 9, 8, 9, 1, 4, 3, 0, 4, 0, 1, 3, 1, 8, 2, 6, 8, 7, 4, 4, 6, 7, 2, 4, 1, 9, 4, 5, 7, 8, 5, 1, 6, 3, 2, 3, 8, 7, 4, 9, 1, 9, 8, 5, 8, 8, 7, 5, 2, 2, 9, 2, 2, 2, 7, 2, 5, 9, 4, 1, 7, 6, 4, 1, 7, 8, 8, 8, 7, 0, 7, 8, 5, 2, 7, 8, 5, 7
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OFFSET
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0,1
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COMMENTS
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For many choices of a,b,c, there is exactly one x>0 satisfying a*x^2+b*x*sin(x)=c*cos(x).
Guide to related sequences, with graphs included in Mathematica programs:
a.... b.... c.... x
Suppose that f(x,u,v) is a function of three real variables and that g(u,v) is a function defined implicitly by f(g(u,v),u,v)=0. We call the graph of z=g(u,v) an implicit surface of f.
For an example related to A199429, take f(x,u,v)=x^2+u*x*sin(x)-v*cos(x) and g(u,v) = a nonzero solution x of f(x,u,v)=0. If there is more than one nonzero solution, care must be taken to ensure that the resulting function g(u,v) is single-valued and continuous. A portion of an implicit surface is plotted by Program 2 in the Mathematica section.
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LINKS
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EXAMPLE
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x=0.6434363641380261586420989143040131826874...
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MATHEMATICA
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a = 1; b = 1; c = 1;
f[x_] := a*x^2 + b*x*Sin[x]; g[x_] := c*Cos[x]
Plot[{f[x], g[x]}, {x, -2 Pi, 2 Pi}, {AxesOrigin -> {0, 0}}]
r = x /. FindRoot[f[x] == g[x], {x, .64, .65}, WorkingPrecision -> 110]
(* Program 2: implicit surface: x^2+u*x*sin(x)=v*cos(x) *)
f[{x_, u_, v_}] := x^2 + u*x*Sin[x] - v*Cos[x];
t = Table[{u, v, x /. FindRoot[f[{x, u, v}] == 0, {x, 0, 1}]}, {u, 0, 10}, {v, u, 100}];
ListPlot3D[Flatten[t, 1]] (* for A199429 *)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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