原式=4a²-4ab+b²+3b²+12b+12+4c²-8c+4=0=(2a-b)²+3(b+2)²+4(c-1)²=0∴(2a-b)²≥0,3(b+2)²≥0,4(c-1)²≥0∴2a-b=0, b+2=0, c-1=0 ...