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SolveAFunctionOfTheHyperbolicTangent​(AngouriMath.​Entity,​AngouriMath.​Entity.​Variable,​System.​Boolean)

 Method (no overloads)

Summary

A function of the hyperbolic tangent of a linear, under u = tanh(a + b x): the parser
writes tanh(L) as (W - 1)/(W + 1) and coth(L) as (W + 1)/(W - 1) with W = e^(2 L), so an integrand built from those alone is R(u), and
dx = du/(b (1 - u^2)). tanh(x)/sqrt(a + b tanh(x)^2 + c tanh(x)^4) is
u/((1 - u^2) sqrt(a + b u^2 + c u^4)), and sin(tanh(x)) is
sin(u)/(1 - u^2), onto the sine and cosine integrals. The trigonometric
counterparts are answered under u = tan(x), which the substitution reads in the
tangent as a node; the hyperbolic functions arrive as exponentials, and nothing read them
as a tangent. Rubi's 6.3 and 6.4.
https://github.com/asc-community/AngouriMath/issues/233

Remarks

Only where R is not a rational function: those the exponential substitution answers,
and so a power of a + a coth(L) or a - a coth(L) alone, a binomial in W.
Every exponential has to be a whole power of W inside one of the two quotients;
one anywhere else, an odd power of e^L from a sinh or cosh among
them, and the rule declines. d/dx F(tanh(L)) = b (1 - tanh(L)^2) F'(tanh(L)) wherever F is differentiable, so the answer written back holds where the integrand
is defined -- and says nothing where the conditions of F fail for every u in
(-1, 1), which is the rule's to decline.

























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