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A198414
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Decimal expansion of x > 0 satisfying x^2 = 2*sin(x).
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107
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1, 4, 0, 4, 4, 1, 4, 8, 2, 4, 0, 9, 2, 4, 3, 4, 3, 6, 4, 1, 4, 8, 3, 2, 7, 9, 4, 3, 7, 4, 5, 7, 5, 8, 6, 0, 3, 7, 2, 5, 7, 1, 6, 1, 3, 7, 0, 4, 9, 1, 1, 4, 8, 1, 0, 9, 4, 4, 8, 2, 4, 3, 5, 4, 8, 7, 7, 5, 2, 5, 2, 9, 5, 6, 1, 7, 1, 4, 4, 3, 6, 2, 1, 2, 0, 5, 1, 0, 1, 5, 2, 4, 8, 2, 0, 8, 1, 7, 5
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OFFSET
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1,2
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COMMENTS
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For many choices of a,b,c, there is a unique nonzero number x satisfying a*x^2+b*x=c*sin(x).
Specifically, for a>0 and many choices of b and c, the curves y=ax^2+bx and y=c*sin(x) meet in a single point if and only if b=c, in which case the curves have a common tangent line, y=c*x. If b<c, the curves meet in quadrant 1; if b>c, they meet in quadrant 2.
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 A198414, take f(x,u,v)=x^2+u*x-v*sin(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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1.4044148240924343641483279437457586037...
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MATHEMATICA
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a = 1; b = 0; c = 2;
f[x_] := a*x^2 + b*x; g[x_] := c*Sin[x]
Plot[{f[x], g[x]}, {x, -1, 2}]
r = x /. FindRoot[f[x] == g[x], {x, 1.4, 1.41}, WorkingPrecision -> 110]
(* Program 2: an implicit surface of x^2+u*x=v*sin(x) *)
f[{x_, u_, v_}] := x^2 + u*x - v*Sin[x];
t = Table[{u, v, x /. FindRoot[f[{x, u, v}] == 0, {x, .01, 6}]}, {u, .1, 100}, {v, u, 100}];
ListPlot3D[Flatten[t, 1]]
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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