用配方法证明-10x²+7x-4的值恒小于0

用配方法证明-10x²+7x-4的值恒小于0
用配方法证明-10x²+7x-4的值恒小于0

用配方法证明-10x²+7x-4的值恒小于0
证：
-10x²+7x-4
=-10(x-7/20)²-4+49/40
=-10(x-7/20)²-151/40
=-[10(x-7/20)²+151/40]
平方项非负,10(x-7/20)²≥0 10(x-7/20)²+151/40≥151/40>0
-[10(x-7/20)²+151/40]