判断代数式-10x^2+7x-4的符号

结果一定是负数,这个应该是高中数学内容-10x^2+7x-4= -10(x^2-0.7x)-4= -10(x^2-2*0.35*x+0.35^2-0.35^2)-4= -10(x^2-2*0.35*x+0.35^2)+10*0.35^2-4= -10(x-0.35)^2+1.225-4= -10(x-0.35)^2-2.775因为(x-0.35)^2必定...