Real roots for X^3+x+1=0?
| 1)问A是否大于零，A.X^3<0; B. X^3+x+1=0
和老JJ不同，老机经是X^2+X+1=0
[思路] X^3+x+1=0
x(x^2+1)+1=0
x(x^2+1)=-1
x^2+1>0
x<0
[确认]D
For this question, if you plot the graph of x^3+x+1=0 using a graphical calculator, there is only one real root for this equation, the other two should be imaginary roots. So I think the answer for this one is still A. The second condition only tells that there is one X is less than 0, not all X. |
