∵x²+y²+5/4=2x+y→x²-2x+y²-y+5/4=0→（x-1）²+（y-1/2）²=0→x=1,y=1/2∴（x+y)·xy=（1+1/2）-1*1/2=1∵a²+b²+c²=ab+bc+ac→2a²+2b²+2c²=2ab+2bc+2...