证明：-10x²+7x-4=-10[x²-(7/10)x+(2/5)]=-10[x²-(7/10)x+(7/20)²-(7/20)²+(2/5)]=-10{[x²-(7/10)x+(7/20)²]+[-(7/20)²+(2/5)]}=-10[(x-7/20)²+(111/400)]=-10(x-7/20)²-(111/40)≤-(111/40)＜0希望我的回答对你有帮助，采纳吧O(∩_∩)O！
