Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
5. Solving Polynomial Equations
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Exercise 4 Page 191

Use the Zero Product Property to find the zeros of the polynomial function.

Zeros: x=-3, x=2, and x=0
Graph:

Practice makes perfect

We want to find the zeros and sketch a graph of the given polynomial function. f(x)=x^3+x^2-6x

Zeros of the Function

To do so, we need to find the values of x for which f(x)=0. f(x)=0 ⇔ x^3+x^2-6x=0 To solve the given equation, we will start by factoring out the greatest common factor. Then, we will use the Zero Product Property.
x^3+x^2-6x=0
x( x^2+x-6 )=0
lcx=0 & (I) x^2+x-6=0 & (II)
We can see in Equation (I) that x=0 is a solution for the given equation. To find other solutions, we will solve Equation (II). x^2+x-6=0 Note that the above equation is a quadratic equation. Thus, we can solve it using the Quadratic Formula. ax^2+bx+c=0 ⇔ x=- b±sqrt(b^2-4ac)/2a Let's identify a, b, and c. x^2+x-6=0 ⇔ 1x^2+ 1x+( -6)=0 We see that a= 1, b= 1, and c= -6. Let's substitute these values into the formula, and solve for x.
x=- b±sqrt(b^2-4ac)/2a
x=- 1±sqrt(( 1)^2-4( 1)( -6))/2( 1)
â–Ľ
Solve for x
x=-1±sqrt(1-4(1)(-6))/2(1)
x=-1±sqrt(1-4(-6))/2
x=-1±sqrt(1+24)/2
x=-1±sqrt(25)/2
x=-1 ± 5/2
The solutions for this equation are x= -1± 52. Let's separate them by using the positive and negative signs.
x=-1± 5/2
x=-1+5/2 x=-1-5/2
x=4/2 x=-6/2
x=2 x=-3

We found that the zeros of f(x)=x^3+x^2-6x are x=- 3, x=2, and x=0.

Graph

To draw the graph of the function, we will find some additional points and consider the end behavior. Let's use a table to find additional points.

x x^3+x^2-6x f(x)=x^3+x^2-6x
- 2 ( - 2)^3+( - 2)^2-6( - 2) 8
1 1^3+( 1)^2-6( 1) - 4
3 3^3+( 3)^2-6( 3) 18

The points ( - 2, 8), ( 1, - 4), and ( 3, 18) are on the graph of the function. We can also see that the leading coefficient is 1, which is a positive number. Also, the degree is 3, which is an odd number. Therefore, the end behavior is down and up. Now, let's draw the graph!