Step 1: Using Descartes' Rule of Signs

Positive Roots

Descartes' Rule of Signs states that the number of positive real roots of a polynomial is equal to the number of sign changes between consecutive non-zero terms in the polynomial or less than that by an even number.

For the polynomial $f(x) = 2x^4 - x^3 + 4x^2 - 5x + 1$, let’s check the signs of the coefficients:

• $2x^4$ (positive)
• $-x^3$ (negative)
• $+4x^2$ (positive)
• $-5x$ (negative)
• $+1$ (positive)

The sequence of signs is: $+, -, +, -, +$.

There are 4 sign changes, so the possible number of positive real roots is:

• 4 (or)
• 2 (or)
• 0 (subtracting even numbers)

Negative Roots

To estimate the number of negative real roots, we apply Descartes' Rule of Signs to $f(-x)$.

We substitute $-x$ into the polynomial:

= 2x^4 + x^3 + 4x^2 + 5x + 1$$ Now, check the signs of the new polynomial $$f(-x) = 2x^4 + x^3 + 4x^2 + 5x + 1$$: - $$2x^4$$ (positive) - $$+x^3$$ (positive) - $$+4x^2$$ (positive) - $$+5x$$ (positive) - $$+1$$ (positive) There are **no** sign changes, so there are 0 negative real roots. ### Step 2: Solve the Polynomial Equation Now we solve the equation $$2x^4 - x^3 + 4x^2 - 5x + 1 = 0$$. Finding the exact roots of a quartic equation like this is non-trivial algebraically, so numerical methods or graphing techniques can be used to find approximate solutions. Would you like me to proceed with solving this equation using numerical methods (such as Newton’s method or graphing), or would you prefer a more detailed analysis of the function's behavior? --- ### Additional Questions: 1. How do numerical methods like Newton's method help in solving polynomial equations? 2. Can Descartes' Rule of Signs indicate complex roots? 3. What does it mean if there are no sign changes for $$f(-x)$$? 4. How can synthetic division help in finding polynomial roots? 5. Are there other rules to estimate root behavior beyond Descartes’ Rule of Signs? **Tip:** When using Descartes' Rule of Signs, always remember that it only estimates the number of real roots, and complex roots must be considered separately.