Hello, landlord, I have questions about your level. If you do not understand this step, can you understand the ultimate value of OA? My feeling is, if you understand this step, or you don't understand the next step, well, don't talk nonsense, because there are conditions (x-a) 2+y 2 =1x 2+(y-b) 2 =1.

= Under the radical sign (1/2)+1/2)+(2ax+2by-a2-b2) =1

And 2ax+2by-a2-B2 = (x-a) 2+(y-b) 2-(x2+y2).

Bring 2ax+2by-a2-b2 = (x-a) 2+(y-b) 2-(x 2+y 2) into the picture, and the result is