Chapter 4.1, Problem 18E

To determine

To describe: the end behavior of the graph of given polynomial function.

Answer to Problem 18E

  $g\left(x\right)\to -\infty$ as $x\to -\infty$ and $g\left(x\right)\to \infty$ as $x\to +\infty$ .

Explanation of Solution

Given information:

A function is given as

  $g\left(x\right)=7x^7+12x^5-6x^3-2x-18$

Concept used:

A polynomial function is of the form

  $f\left(x\right)=a_n{x}^n+a_{n-1}{x}^{n-1}+\mathrm{...}+a_{1}x+a_0$

Terms of a polynomial function should be arranged in descending order according to its degree to express it in a standard form and degree of each term should be a positive integer or whole number. The coefficients should be real numbers.

Leading coefficient of a polynomial function is the coefficient of the leading term.

Degree of the polynomial is the degree of leading term or the height degree in the polynomial function.

For the polynomial $f\left(x\right)=a_n{x}^n+a_{n-1}{x}^{n-1}+\mathrm{...}+a_{1}x+a_0$ the leading coefficient is $a_n$ and the degree is $n$ .

The end behavior can describe the graph of a polynomial function as  $x$  approaches $+\infty$ or as  $x$  approaches $-\infty$ .

The end behavior of a polynomial function can be determined by the leading coefficient and the degree of the polynomial.

If degree is even and leading coefficient is negative.

  $f\left(x\right)\to -\infty$ as $x\to -\infty$ and $f\left(x\right)\to -\infty$ as $x\to +\infty$ .

If degree is odd and leading coefficient is negative.

  $f\left(x\right)\to \infty$ as $x\to -\infty$ and $f\left(x\right)\to -\infty$ as $x\to +\infty$ .

If degree is odd and leading coefficient is positive.

  $f\left(x\right)\to -\infty$ as $x\to -\infty$ and $f\left(x\right)\to \infty$ as $x\to +\infty$ .

If degree is even and leading coefficient is positive.

  $f\left(x\right)\to \infty$ as $x\to -\infty$ and $f\left(x\right)\to \infty$ as $x\to +\infty$ .

Calculation:

Consider the given function.

  $g\left(x\right)=7x^7+12x^5-6x^3-2x-18$

Now, degree of each term is a whole number and all coefficients are real.

So, the function is polynomial function.

Now, degree of the polynomial function is 7.

Leading term is $7x^7$ .

So, leading coefficient will be $7$ .

Degree is odd and leading coefficient is positive.

  $g\left(x\right)\to -\infty$ as $x\to -\infty$ and $g\left(x\right)\to \infty$ as $x\to +\infty$ .

Hence, the end behavior is $g\left(x\right)\to -\infty$ as $x\to -\infty$ and $g\left(x\right)\to \infty$ as $x\to +\infty$ .