This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A199269 #8 Feb 07 2025 16:44:05
%S A199269 1,0,1,7,2,4,0,7,9,8,3,4,2,4,5,5,5,6,6,5,6,0,3,5,0,0,7,0,5,4,5,3,4,6,
%T A199269 1,7,6,0,1,7,4,1,1,4,3,2,0,8,0,3,7,3,2,1,9,3,7,7,8,9,5,6,5,4,8,8,6,6,
%U A199269 5,8,0,6,3,8,8,8,7,4,9,9,0,9,7,6,3,7,3,1,6,8,2,8,8,1,9,1,9,0,0
%N A199269 Decimal expansion of x<0 satisfying 2*x^2+2*x*cos(x)=1.
%C A199269 See A199170 for a guide to related sequences. The Mathematica program includes a graph.
%H A199269 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>.
%e A199269 negative: -1.017240798342455566560350070545346176017411...
%e A199269 positive: 0.381748420992985957918521611823486645593341...
%t A199269 a = 2; b = 2; c = 1;
%t A199269 f[x_] := a*x^2 + b*x*Cos[x]; g[x_] := c
%t A199269 Plot[{f[x], g[x]}, {x, -3, 3}, {AxesOrigin -> {0, 0}}]
%t A199269 r = x /. FindRoot[f[x] == g[x], {x, -1.1, -1.0}, WorkingPrecision -> 110]
%t A199269 RealDigits[r] (* A199269 *)
%t A199269 r = x /. FindRoot[f[x] == g[x], {x, .38, .39}, WorkingPrecision -> 110]
%t A199269 RealDigits[r] (* A199270 *)
%Y A199269 Cf. A199170.
%K A199269 nonn,cons
%O A199269 1,4
%A A199269 _Clark Kimberling_, Nov 04 2011