This is the sign of the partial derivative of the function f(x, y) to x:? f(x，y)/？ x；

'?' The pronunciation of "Luan" is "Luan", which is Chinese pinyin.

For example: f(x, y)=x+x? y+y？

So: f(x, y)/? X= 1+2xy //: When taking the partial derivative of x, take y as a constant; When calculating the partial derivative of y, x is regarded as a constant;

? f(x，y)/？ y=x？ +2y。

"Partial derivative" in English: "Partial derivative"

Partial derivative is also called' partial WeChat service'.