由f(1)=a/2 => a/2=a+b+c => -b = a/2+cb²-4ac=a²/4+c²+ac-4ac=a²/4+c²-3aca²/4+9a²/4-9a²/4-3ac+c²=-2a²+(3a/2-c)²靠 是不是题目错了啊...莫不是设函数f(x...