1. Find the area of a curved fence, whose base is the upper half of the circle of radius 4 centered at the origin, and whose height is given by the function f(x, y)-xy

2. Consider the line integral c (x,y) ds, where C represents a curved wire in the x-y plane, and (x,y) represents the density of the wire at any given point. Explain what ds represents geometrically, what physical meaning f (x, y) ds has, and what physical meaning the integral has.