(a-c)(b-c)=0

= & gta.b-a.c-c.b+c^2=0

= & gt2+c^2=c.(a+b)<； =4c

= & gtc^2-4c+2<； =0

=> | c | min = (radical number 2 of 4-2)/2 =2- radical number 2

Hello, Baidu expert group is happy to answer your questions. If you find it helpful, please adopt it. Thank you!