<p>设二元函数<img src="https://learnfile.20230611.cn/learnAppQuestion/34/d0/34d03439cef9ed334dde87936ec6e5e3.jpg" style="width: 100%;height: auto;">则<img src="https://learnfile.20230611.cn/learnAppQuestion/43/e9/43e922262e6b4e0be049da7b24681ac2.jpg" style