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# What if the fourth derivative of a polynomial is zero?

Updated: 11/1/2022 Wiki User

12y ago

There are many things that can be said about a polynomial function if its fourth derivative is zero, but the main thing you can know about this function from this information is that its order is 3 or less.

Consider an nth order polynomial with only positive exponents:

axn + bxn-1 + ... + cx2 + dx + e

As you derive this function, its derivatives will eventually be equal to zero. The number of derivatives that are nonzero before they all become zero can tell you what order the polynomial function was. Consider an example, y = x4.

y = x4

y' = 4x3

y'' = 12x2

y''' = 24x

y(4) = 24

y(5) = 0

The original polynomial was of order 4, and its derivatives were nonzero up until its fifth derivative. From this, you can generalize to say that any function whose fifth derivative is equal to zero is of order 4 or less. If the function was of higher order than 4, its derivatives would not become zero until later. If the function was of lower order than 4, its fifth derivative would still be zero, but it would not be the first zero-valued derivative.

So this experimentation yielded a rule that the first zero-valued derivative is one greater than the order of the polynomial. Your problem states that some polynomial has a fourth derivative that is zero. Our working rule states that this polynomial can be of highest order 3.

So, your polynomial can be, at most, of the form:

y = ax3 + bx2 + cx + d

Letting the constants a through d be any real number (including zero), this general form expresses any polynomial that will satisfy your condition. Wiki User

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Q: What if the fourth derivative of a polynomial is zero?
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Yes.

### Is it always true that for any polynomial px if x is a zero of the derivative then x px is a maximum or minimum value of px?

No. The important decider is the second derivative of the polynomial (the gradient of the gradient of the polynomial) at the zero of the first derivative: If less than zero, then the point is a maximum If more than zero, then the point in a minimum If equal to zero, then the point is a point of inflection. Consider the polynomial f(x) = x3, then f'(x) = 3x2 f'(0) = 0 -&gt; x = 0 could be a maximum, minimum or point of inflection. f''(x) = 6x f''(0) = 0 -&gt; x = 0 is a point of inflection Points of inflection do not necessarily have a zero gradient, unlike maxima and minima which must. Points of inflection are the zeros of the second derivative of the polynomial.

### Is it always true that between any two zeros of the derivative of any polynomial there is a zero of the polynomial?

No. Consider the polynomial: f(x) = x3 + 4x2 + 4x + 16 then f'(x) = 3x2 + 8x + 4 = (3x + 2)(x + 2) =&gt; x = -2/3, -2 are the zeros of f'(x) Using the second derivative: f''(x) = 6x + 8 it can be seen that: f''(-2) = -4 -&gt; x = -2 is a maximum f''(-2/3) = +4 -&gt; x = -2/3 is a minimum But plugging back into the original polynomial: f(-2) = 16 f(-2/3) = 14 22/27 Between the zeros of the first derivative, the slope of the polynomial is negative so that the polynomial is always decreasing in value, but as the polynomial is greater than zero at the zeros of the first derivative, it cannot become zero between them. That is it has no zeros between the zeros of its first derivative f(x) = x3 + 4x2 + 4x + 16 = (x + 4)(x2 + 4) has only 1 zero at x = -4.

### Is it always true that the zeros of the derivative and the zeros of the polynomial always alternate in location along the horizontal axis?

A zero of the derivative will always appear between two zeroes of the polynomial. However, they do not always alternate. Sometimes two or more zeroes of the derivative will occur between two zeroes of a polynomial. This is often seen with quartic or quintic polynomials (polynomials with the highest exponent of 4th or 5th power).

### How do you do a polynomial?

Basically the same way you graph most functions. You can calculate pairs of value - you express the polynomial as y = p(x), that is, the y-values are calculated on the basis of the x-values, you assign different values for "x", and calculate the corresponding values for "y". Then graph them. You can get more information about a polynomial if you know calculus. Calculus books sometimes have a chapter on graphing equations. For example: if you calculate the derivative of a polynomial and then calculate when this derivate is equal to zero, you will find the points at which the polynomial may have maximum or minimum values, and if you calculate the derivative at any point, you'll see whether the polynomial increases or decreases at that point (from left to right), depending on whether the derivative is positive or negative. Also, if you calculate when the second derivative is equal to zero, you'll find points at which the polynomial may change from convex to concave or vice-versa.

### How do you graph a polynomial?

Basically the same way you graph most functions. You can calculate pairs of value - you express the polynomial as y = p(x), that is, the y-values are calculated on the basis of the x-values, you assign different values for "x", and calculate the corresponding values for "y". Then graph them. You can get more information about a polynomial if you know calculus. Calculus books sometimes have a chapter on graphing equations. For example: if you calculate the derivative of a polynomial and then calculate when this derivate is equal to zero, you will find the points at which the polynomial may have maximum or minimum values, and if you calculate the derivative at any point, you'll see whether the polynomial increases or decreases at that point (from left to right), depending on whether the derivative is positive or negative. Also, if you calculate when the second derivative is equal to zero, you'll find points at which the polynomial may change from convex to concave or vice-versa.

### What is the definition for the zero of a polynomial function?

The zero of a polynomial in the variable x, is a value of x for which the polynomial is zero. It is a value where the graph of the polynomial intersects the x-axis.

### What is the derivative of 40?

The derivative of 40 is zero. The derivative of any constant is zero.

They tell you where the graph of the polynomial crosses the x-axis.Now, taking the derivative of the polynomial and setting that answer to zero tells you where the localized maximum and minimum values occur. Two values that have vast applications in almost any profession that uses statistics.

### What type of polynomial is formed by adding a second degree binomial to a fourth degree monomial. State the degree of this polynomial?

A fourth degree polynomial.

### What is the derivative of 4pi?

zero. In this problem, since there is no variable, the derivative is zero.

### What is the derivative of 8?

Zero. In general, the derivative of any constant is zero.