Question 1134148: Indentify the number of positive, negative, and imaginary roots, all rational roots , and the total amount of roots.
x^3+x-6=0
Found 2 solutions by MathLover1, ikleyn: Answer by MathLover1(20849) (Show Source): Answer by ikleyn(52776) (Show Source):
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The polynomial on the left side is of degree 3 - so the total amount of the roots is 3.
It includes real and complex number roots.
The derivative of the left side polynomial is 3x^2 + 1; from the first glance,
it is clear that this derivative function is always positive - so the original
polynomial function on the left side is monotonically increasing.
It means, that there is ONLY ONE real root. Hence, other two roots are complex numbers.
At x= 0, the left side function has the value of -6, and it rises monotonically to +infinity as x --> oo -
hence, the real root is a positive real number.
Then, according to the Rational Root theorem, rational roots can be only among these numbers (divisors of 6): 1, 2, 3 or 6.
But easy mental check shows that the number 2 is not the root, and, moreover, at x= 2 the left side function is just positive,
so the only real root is IRRATIONAL number between 1 and 2.
So, the required analysis is COMPLETED, and its results are as follows:
- total number of roots is 3;
- there is only one real root;
- there are two complex roots;
- the real root is positive;
- the number of positive real roots is 1;
- the number of negative real roots is zero;
- the number of rational real roots is zero.
All the questions are answered; so the solution is completed.
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