題目 Problem 8. Find the work done by the force F=xyi+(y−x)j\mathbf{F}=xy\mathbf{i}+(y-x)\mathbf{j}F=xyi+(y−x)j over the straight line from (1,1)(1,1)(1,1) to (2,3)(2,3)(2,3). Answer : \underline{\quad(1)\quad} 解答