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
-10x²+7x-4
=-10(x²-7/10x)-4
=-10(x²-7/10x+49/400)-111/40
=-10(x-7/20)²-111/40
∵-10(x-7/20)²≠0
∵-10(x-7/20)²-111/40＜0
∴-10x²+7x-4的值恒小于0