If (cosx)y=(siny)x, then dydx=

${(\cos x)}^{y} = {(\sin y)}^{x}$

$y . \log (\cos x) = x . \log (\sin y)$

$y . \frac{1}{\cos x} (- \sin x) + y' . \log (\cos x) = x \frac{\cos y}{\sin y} . y' + \log (\sin y)$

$y^{|} [logcos x - x . \frac{\cos y}{\sin y}] = y . \frac{\sin x}{\cos x} + \log (\sin y)$

$y^{|} [logcos x - x \cot y] = y . \tan x + \log (\sin y)$

$y^{|} = \frac{logsin y + y \tan x}{logcos x - x . \cot y}$

If ${(\cos x)}^{y} = {(\sin y)}^{x}$ , then $\frac{d y}{d x} =$