There are two stationary fields of force F=ayi\mathbf{F}=a y \mathbf{i}F=ayi and F\mathbf{F}F =axi+byj,=a x \mathbf{i}+b y \mathbf{j},=axi+byj, where i\mathbf{i}i and j\mathbf{j}j are the unit vectors of the xxx and yyy axes, and aaa and bbb are constants. Find out whether these fields are potential.