Answer
$du=\dfrac{e^{2t}}{(1+se^{2t})}ds+\dfrac{2se^{2t}}{(1+se^{2t})}dt$
Work Step by Step
Given: $u=ln(1+se^{2t})$
$du=f_s(s,t)ds+f_t(s,t)dt$
Thus,
$du=\dfrac{e^{2t}}{(1+se^{2t})}ds+\dfrac{2se^{2t}}{(1+se^{2t})}dt$
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