# The derivative of $f(t, y(t))$ with respect to $t$?

Given a function $f(t, y(t))$, how can I express its derivative with respect to $t$ and $d f/{d t}$?

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Suppose $x = x(s,t)$, and $y = y(s,t)$, the chain rule for two variables is
What happens if $x(s,t) = t$ and $y(s,t) = y(t)$?