1. The problem statement, all variables and given/known data A small block with mass 0.0400 kg is moving in the xy-plane. The net force on the block is described by the potential-energy function U(x, y) = (5.80 J/m2)x2-(3.60 J/m3)y3. What are the magnitude and direction of the acceleration of the block when it is at the point (x = 0.300 m, y = 0.600 m)? 2. Relevant equations U(x, y) = (5.80 J/m2)x2-(3.60 J/m3)y3 3. The attempt at a solution I've attached the solution as an image; it was given to me with the question. Why does the x-component of acceleration becomes positive when plugged into arctan to find the angle?