Question

Let xy=1

and let dy/dt=5

Find dx/dt when x=5

Answer 1

Hint:

\[\Large y = {1\over x}\]
\[\Large {dy\over dt} = x\]
\[\Large {d\over dt} {1\over x} = x\]

Answer 2

(Notice I substituted in \(y = {1\over x}\) into the second equation to get the third?