並前往https://ocw.nthu.edu.tw/ocw/upload/7/news/L17_critical%20point(%E8%87%A8%E7%95%8C%E9%BB%9E)%20First%20derivative%20test(%E4%B8%80%E9%9A%8E%E5%B0%8E%E5%87%BD%E6%95%B8%E6%B8%AC%E8%A9%A6)%20Second%20derivative%20test(%E4%BA%8C%E9%9A%8E%E5%B0%8E%E5%87%BD%E6%95%B8%E6%B8%AC%E8%A9%A6)%204.6%20Concavity%20and%20points%20of%20inflection(%E5%9C%96%E5%BD%A2%E5%87%B9%E6%80%A7%E5%92%8C%E5%8F%8D%E6%9B%B2%E9%BB%9E)%20Concave%20up%20and%20concave%20down.pdf
