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 A198139 #6 Feb 07 2025 16:44:05
%S A198139 5,8,1,7,2,0,0,7,9,7,3,1,6,5,9,7,2,2,8,4,2,8,6,5,9,2,3,2,7,1,4,8,8,2,
%T A198139 7,4,9,0,7,5,9,9,1,9,8,4,9,2,8,9,2,5,9,8,6,9,8,4,4,3,4,7,2,5,8,1,1,3,
%U A198139 0,3,7,5,4,1,9,5,2,2,4,1,8,7,9,2,9,8,8,4,1,3,4,0,5,2,8,0,4,1,1
%N A198139 Decimal expansion of greatest x having 3*x^2+4x=4*cos(x).
%C A198139 See A197737 for a guide to related sequences. The Mathematica program includes a graph.
%e A198139 least x: -1.447057151041655078779471681449880627...
%e A198139 greatest x: 0.58172007973165972284286592327148827490...
%t A198139 a = 3; b = 4; c = 4;
%t A198139 f[x_] := a*x^2 + b*x; g[x_] := c*Cos[x]
%t A198139 Plot[{f[x], g[x]}, {x, -2, 1}]
%t A198139 r1 = x /. FindRoot[f[x] == g[x], {x, -1.5, -1.4}, WorkingPrecision -> 110]
%t A198139 RealDigits[r1] (* A198138 *)
%t A198139 r2 = x /. FindRoot[f[x] == g[x], {x, .58, .59}, WorkingPrecision -> 110]
%t A198139 RealDigits[r2] (* A198139 *)
%Y A198139 Cf. A197737.
%K A198139 nonn,cons
%O A198139 0,1
%A A198139 _Clark Kimberling_, Oct 23 2011