判断代数式-10x^2+7x-4的符号

判断代数式-10x^2+7x-4的符号
判断代数式-10x^2+7x-4的符号

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必定大于等于0,-10(x-0.35)^2就必定小于等于0,然后再-2.775,结果一定是

=-10(X2-0.7X+0.35*0.35)+10*0.35*0.35-4=-10(X-0.35)2+3.5*0.35-4<0