Section 1.3 Problems 測試是否為正合 In each of Problems 1-5, test the differential equation for exactness. If it is exact in some region R of the plane, find a potential function and a general solution, perhaps implicitly defined, that is valid for that region. If it is not exact on any region, do not attempt a solution. 1. 2y² + yexy + (4xy + xexy + 2y)y' = 0 2. 4xy + 2x + (2x² + 3y²)y' = 0 3. 4xy + 2x²y + (2x² + 3y²)y' = 0 4.2 cos(x+y) - 2x sin(x + y) - 2x sin(x + y)y' = 0 tlsx9 ² +y+ (3y² + x)y' = 0 5.