Chapter 2.2, Problem 100E

a.

To determine

To find:The interval of unit length in which zero of the given polynomial function lie definitely, using Intermediate Value Theorem and graphing utility.

Answer to Problem 100E

The required intervals are $\left[-2,-1\right]$ , $\left[1,2\right]$ and $\left[3,4\right]$ .

Explanation of Solution

Given:

The polynomial function is $f\left(x\right)=x^3-4x^2-2x+10$ .

Formula/ concept used:

The Intermediate Value Theorem states that $f\left(b\right)$ Let “ a ” and “ b ”be real numbers such that $a<b$ . If a polynomial function such that $f\left(a\right)\ne f\left(b\right)$ , then in interval $\left[a,b\right]$ takes on every value between $f\left(a\right)$ and $f\left(b\right)$ . If $f\left(a\right)$ and $f\left(b\right)$ are of opposite sign then a zeros surely lie in interval $\left[a,b\right]$ .

Graph:

The graph of function $f\left(x\right)=x^3-4x^2-2x+10$ is shown in Figure-1 here.

We have $f(a=-2)=-10$ and $f(b=-1)=7$ , thus $f\left(-2\right)<0$ and $f\left(-1\right)>0$ , hence, there exists a zero of $f\left(x\right)=x^3-4x^2-2x+10$ in the intervalof unit length $\left[-2,-1\right]$ .We see that $f\left(-1.537\right)=0$ , i.e., $x=-1.537$ is zero of polynomial function $f\left(x\right)=x^3-4x^2-2x+10$ .

  

We have $f(a=1)=5$ and $f(b=2)=-2$ , thus $f\left(1\right)>0$ and $f(2)<0$ , hence, there exists a zero of $f\left(x\right)=x^3-4x^2-2x+10$ in the intervalof unit length $\left[1,2\right]$ .We see that $f\left(1.693\right)=0$ , i.e., $x=1.693$ is zero of polynomial function $f\left(x\right)=x^3-4x^2-2x+10$ .

We have $f(a=3)=-5$ and $f(b=4)=2$ , thus $f\left(3\right)<0$ and $f(4)>0$ , hence, there exists a zero of $f\left(x\right)=x^3-4x^2-2x+10$ in the intervalof unit length $\left[3,4\right]$ .We see that $f\left(3.843\right)=0$ , i.e., $x=3.843$ is zero of polynomial function $f\left(x\right)=x^3-4x^2-2x+10$ .

Conclusion:

There exists a zero of $f\left(x\right)=x^3-4x^2-2x+10$ in each intervals $\left[-2,-1\right]$ , $\left[1,2\right]$ and $\left[3,4\right]$ .

b.

To determine

To find: The real zeros of polynomial function given in part (a) using graphing utility.

Answer to Problem 100E

The zeros of function $f\left(x\right)=x^3-4x^2-2x+10$ are $x=-1.537$ , $x=1.693$ and $x=3.843$ .

Explanation of Solution

Given:

The polynomial function and the graph of function $f\left(x\right)=x^3-4x^2-2x+10$ in part (a).

Concept used:

The value of x where the graph of function intersect or touch the x -axis is the zero of function.

Calculations:

From graph Figure-1, in part (a) we see that graph of function $f\left(x\right)$ intersect x -axis at points $\left(-1.537,0\right)$ , $\left(1.693,0\right)$ and $\left(3.843,0\right)$ .

Hence, $x=-1.537$ , $x=1.693$ and $x=3.843$ are zeros of function $f\left(x\right)=x^3-4x^2-2x+10$ .

Conclusion:

The points $x=-1.537$ , $x=1.693$ and $x=3.843$ are zeros of function $f\left(x\right)=x^3-4x^2-2x+10$ .

c.

To determine

To verify: The answers of part (a) using table feature of graphing utility.

Explanation of Solution

Given:

The zeros of function $f\left(x\right)=x^3-4x^2-2x+10$ lie in intervals $\left[-2,-1\right]$ , $\left[1,2\right]$ and $\left[3,4\right]$ .

Verification:

From the graph in Figure-1, we obtain a table of some solutions of the given polynomial function $f\left(x\right)=x^3-4x^2-2x+10$ as:

  

There is change of the function $f\left(x\right)$ in intervals $\left[-2,-1\right]$ , $\left[1,2\right]$ and $\left[3,4\right]$ each of length 1, these results are same as of part (a).

Thus, the results of part (a) stands verified.