1.a=b?题目有没核凳问题宴氏明?2.a2+b2+c2+d2=r2+R2,(a-c)2+(b-d)2+2ac+2bd=r2+R2,(a-c)2>晌告=0,(b-d)2>=0,r2+R2-2(ac+bd)>=0,r2+R2>=2(ac+bd),ac+bd<=(r2+R2)/2