Question

Determine (a) the maximum number of turning points of the graph of the function and (b) the maximum number of real zeros of the function. $$f(x)=-x^{5}+x^{4}-x$$

Short answer

The maximum number of turning points of the graph of the given function is 4, and the maximum number of real zeros of the given function is 5.

Step-by-step solution

Determine the Maximum Number of Turning Points

A polynomial function's turning points are found using the formula of degree-1. Here, the given function is 5th degree polynomial, so the maximum number of turning points can be 5-1=4. Therefore, the graph of the given function has at most 4 turning points.

Determine the Maximum Number of Real zeros

For a polynomial function, its real zeros is equal to the degree of the polynomial. Therefore, the given function is a 5th degree polynomial, so it can have at most 5 real zeros. These are the maximum possible real values of x where the function equal to zero.

Key concepts

Maximum Turning Points

Understanding the concept of maximum turning points in the context of polynomial functions is vital for students studying algebra and calculus. A turning point is a point at which the graph of the function changes direction from increasing to decreasing or vice versa. The rule of thumb to predict the maximum number of turning points for any polynomial is to take the degree of the polynomial and subtract one. For instance, if we have a 5th-degree polynomial, such as \( f(x) = -x^5 + x^4 - x \), we would expect that there can be up to 4 turning points (\textbackslash\textbackslash( 5-1=4 \textbackslash\textbackslash)).

However, it's important to note that this is the maximum number of turning points—the actual number can be less. Turning points are where the graph of the function has local maxima or minima, which are the top or bottom points of 'hills' and 'valleys' in the curve. Recognizing these points helps in understanding the overall shape and behavior of the graph.

Real Zeros of Polynomial

A real zero of a polynomial is where the graph of the function crosses or touches the x-axis. The significance of these points cannot be overstated as they also correspond to the solutions of the equation \( f(x) = 0 \). A simple way to estimate the number of real zeros is by looking at the degree of the polynomial. A polynomial of degree n can have at most n real zeros. Using our example, \( f(x) = -x^5 + x^4 - x \), being a 5th-degree polynomial, it can have up to 5 real zeros.

However, this is the upper bound of the number of real zeros, and there may be fewer real zeros than the degree suggests. Finding the exact number often requires further evaluation, like factoring, graphing, or using the Rational Root Theorem, to determine the actual zeros the polynomial might have.

Degree of Polynomial Function

The degree of a polynomial function is determined by the highest power of x that appears in the expression. This is a fundamental concept because the degree indicates the utmost behavior of the graph, particularly for large values of x. For example, \( f(x) = -x^5 + x^4 - x \) is a 5th-degree polynomial because the highest exponent of x is 5.

The degree tells us several structural things about the polynomial: the number of possible turning points, the maximum number of real zeros, and hints about the end behavior — whether the function's graph rises or falls as \( x \) goes to infinity or negative infinity. For example, with odd degrees like 5, as \( x \) goes to positive infinity, \( f(x) \) goes to negative infinity (since the leading coefficient is negative), and as \( x \) goes to negative infinity, \( f(x) \) goes to positive infinity.

Graph of Polynomial Function

The graph of a polynomial function provides a visual representation of the function's behavior across its domain. From the graph, one can infer the location of zeros, turning points, and the overall shape of the function. For instance, the shape of the graph for \( f(x) = -x^5 + x^4 - x \) will demonstrate the concept of end behavior—descending to the left and ascending to the right, indicative of an odd-degree polynomial with a negative leading coefficient.

When graphing, look for symmetry, intercepts with the axes, intervals where the function is increasing or decreasing, and places where the function achieves its maximum and minimum values. Key features like y-intercept are found by evaluating \( f(0) \) and the x-intercepts (\textbackslash\textbackslash(the real zeros\textbackslash\textbackslash)) by solving \( f(x) = 0 \). The resulting graph serves as a powerful tool for understanding and solving problems involving polynomial functions.