並前往https://math.ymhs.tyc.edu.tw/masterchen/chenjt99/ScrClass/1091/%E9%AB%98%E4%B8%80%E7%BF%92%E4%BD%9C%E7%94%B2/ch4/4-3%E5%9C%93%E8%88%87%E7%9B%B4%E7%B7%9A%E7%9A%84%E9%97%9C%E4%BF%82.pdf