15. Name the method for solve partial differential equations (PDEQs) that is described below: [DEQ= differential equation] Step 1. Set f(x, y) = u(x)v(y), Step 2. Divide PDEQ by f Step 3. Set purely x-dependent part of resulting equation to a constant to obtain a DEQ for u(x) Step 4. Set purely y-dependent part of resulting equation to a constant to obtain a DEQ for v(y) Step 5. Solve the DEQs obtain in steps 3 & 4