11、设<img src="https://up.zaixiankaoshi.com/docs/77/ab/77ab1500c8e033602a96f29746b34d71.png" alt="77ab1500c8e033602a96f29746b34d71.png">在区间<img src="https://up.zaixiankaoshi.com/docs/3e/79/3e796fa64b82cd924594d296c157bb42.png" alt="3e796fa64b82cd924594d296c157bb42.png">上连续，<img src="https://up.zaixiankaoshi.com/docs/68/95/689593fe85aa969e8898c64a2de74e22.png" alt="689593fe85aa969e8898c64a2de74e22.png">是<img src="https://up.zaixiankaoshi.com/docs/83/c6/83c61e2d1c1e13f5cda324160ff53c32.png" alt="83c61e2d1c1e13f5cda324160ff53c32.png">的内点，如果曲线<img src="https://up.zaixiankaoshi.com/docs/ca/30/ca30d47ce3f6cd237ed2673990ae5dff.png" alt="ca30d47ce3f6cd237ed2673990ae5dff.png">经过<img src="https://up.zaixiankaoshi.com/docs/d0/b9/d0b932cc49c037919487ed98d36a4895.png" alt="d0b932cc49c037919487ed98d36a4895.png">点时，曲线的凹凸性改变了，则称点<img src="https://up.zaixiankaoshi.com/docs/4b/bb/4bbb50cd145664e308b1593e3cdd27ad.png" alt="4bbb50cd145664e308b1593e3cdd27ad.png">为曲线的拐点