‌设函数<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/3057281b4e6c4d088f8a0892174e88b6.png?x-oss-process=image/sharpen,200"/>在点<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/2845cf41546e4cd4835e0201e38cd28f.png?x-oss-process=image/sharpen,200"/>的某邻域内有连续的二阶偏导数，且<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/f3bc2e197ade4df29e0ad8da471ca12c.png?x-oss-process=image/sharpen,200"/>，<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/0df0f00599fc482b96bd437909e1037c.png?x-oss-process=image/sharpen,200"/>，<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/161b67c5115344f5a32b844d6186d586.png?x-oss-process=image/sharpen,200"/>，<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/ca5e9c4a9d844224b048452e1f186853.png?x-oss-process=image/sharpen,200"/>，则在点<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/2845cf41546e4cd4835e0201e38cd28f.png?x-oss-process=image/sharpen,200"/>的该邻域内，（）．‌