Question

初三数学急急急

用配方法证明 5乘（x的平方）-6x+11 的值恒大于0

Answer 1

5x²-6x+11
=5(x²-6x/5)+11
=5(x²-6x/5+9/25)-9/5+11
=5(x-3/5)²+46/5>=46/5>0

Answer 2

5x²-6x+11
=5（x²-6x/5）+11
=5（（x-3/5）²-9/25）+11
=5（x-3/5）²+11-9/5
=5（x-3/5）²+46/5
5（x-3/5）²≥0
46/5＞0
所以5（x-3/5）²+46/5恒大于0

Answer 3

5X^2-6X+11
=5(X^2-6/5X+9/25)+11-9/5
=5(X-3/5)^2+46/5
因为46/5大于0
所以5X^2-6X+11 的值恒大于0

Answer 4

b平方—4ac=36-220<0 所以，无交点，开口向上 值大于 0