UC知道初三因式分解 求证题！
来源：百度知道 编辑：UC知道 时间：2024/06/25 22:12:08
2. 不论x为何实数,多项式3x^2-5x-1的值大于2x^2-4x-7的值.
1. 2x^2+4x+3=2(x^2+2x+1)+1=2(x+1)^2+1>=1>0
2. 3x^2-5x-1-2x^2+4x+7=x^2-x+6=(x-1/2)^2+23/4>=23/4>0
1.2x²+4x+3=2(x²+2x+1)+1=2(x+1)²+1≥1＞0
2.(3x²-5x-1)-(2x²-4x-7)
=x²-x+6
=(x-1/2)²+23/4≥23/4＞0
1.2x^2+4x+3=2（x+1)^2+1>0
2.因为3x^2-5x-1-【2x^2-4x-7】
=x^2-x+6
=（x-1/2)^2+29/4>0
1 2x^2+4x+3=2(x^2+2x)+3
=2[(x+1)^2-1]+3
=2(x+1)^2+1>0
2 (3x^2-5x-1)-(2x^2-4x-7)=x^2-x+6
=(x-0.5)^2+5.75>0
所以(3x^2-5x-1)>(2x^2-4x-7)
1.2x^2+4x+3=2(x^2+2x+1)+1=2(x+1)^2+1
因为2(x+1)^2>=0
所以2(x+1)^2+1>1
2.3x^2-5x-1-(2x^2-4x-7)=x^2-x+6=(x+1/2)^2+23/4
所以原式大于零
1.2x^2+4x+3=2(x^2+2x+1)+1=2(x+1)^2+1>=1>0 所以大于0
2.3x^2-5x-1-2x^2+4x+7=x^2-x+6=(x-1/2)^2+23/4>=23/4>0 2.3x^2-5x-1-2x^2+4x+7=x^2-x+6=(x-1/2)^2