There is such a narrative in junior high school mathematics textbooks; "Compare the sizes of A and B .. You can find the difference between A and B first. Look at this job. It's really something. Negative or zero? ( 1)、 100(x+y)、200、200、( 100/x)+( 100/y)、(x+y)/2、(2xy)/(x+y)，

(2)Q 1-Q2 =(x+y)/2-(2xy)/(x+y)=(x2-2xy+y2)/(2x+2y)=(x-y)2/2(x+y)≥0。

Therefore, if and only if x=y, it is equivalent, otherwise b is equivalent.