Two quantities, x and y, vary with time t. State the differential equation for each of the following.

(a) The rate of change of y with respect to t varies inversely as x.

(b) The rate of change of x with respect to t varies inversely as y. Combining the differential equation of (a) and (b), form a differential equation involving only x and y, solve the differential equation expressing y in terms of x.

How do I combine the two differential equations into one?