The variables x and y are related by `xy=4` .

Take the derivative with respect to t.

=> `x*(dy/dt) + y*(dx/dt) = 0` ...(1)

When x = 2, y = 2. Also `dy/dt = 1` . Substituting these values in (1)

`2*1 + 2*(dy/dt) = 0`

=> `dy/dt = -1`

**The required value of `dy/dt = -1` .**