I have an expression:
$\frac{\sqrt{2} \text{Kf} \left(\cos \left(\sqrt{2} L \sqrt[4]{\frac{B}{\text{Kf}}}\right)+\cosh \left(\sqrt{2} L \sqrt[4]{\frac{B}{\text{Kf}}}\right)\right)}{\left(\frac{B}{\text{Kf}}\right)^{3/4} \left(\sin \left(\sqrt{2} L \sqrt[4]{\frac{B}{\text{Kf}}}\right)+\sinh \left(\sqrt{2} L \sqrt[4]{\frac{B}{\text{Kf}}}\right)\right)}$
(Sqrt[2] Kf (cos(Sqrt[2] L Power[B/Kf, (4)^-1]) +
cosh(Sqrt[2] L Power[B/Kf, (4)^-1])))/((B/Kf)^(
3/4) (sin(Sqrt[2] L Power[B/Kf, (4)^-1]) +
sinh(Sqrt[2] L Power[B/Kf, (4)^-1])))
Obviously there's a pattern: $x = \sqrt[4]{\frac{1}{4}\frac{B}{K_f}}$
x = (B/Kf)^(1/4)/Sqrt[2]
But substituting it with a rule doesn't work:
Well, there's a workaround:
but I hope for a more straightforward approach.