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 3 Page 191

Define another variable to represent x^2.

Zeros: x=- 1 and x=1
Graph:

Practice makes perfect

We want to find the zeros and sketch a graph of the given polynomial function. f(x)=3x^4-6x^2+3

Zeros of the Function

To do so, we need to find the values of x for which f(x)=0. f(x)=0 ⇔ 3x^4-6x^2+3=0 To solve the given equation, we will start by factoring out the greatest common factor.
3x^4-6x^2+3=0
3( x^4-2x^2+1 )=0
x^4-2x^2+1=0
To find solutions, we will need to define another variable. If we let z=x^2, we can rewrite the equation in terms of the z-variable. x^4-2x^2+1=0 ⇔ z^2-2z+1=0 Note that the above equation in terms of z is a quadratic equation. Thus, we can solve it using the Quadratic Formula. az^2+bz+c=0 ⇔ z=- b±sqrt(b^2-4ac)/2a Let's identify a, b, and c. z^2-2z+1=0 ⇔ 1z^2+( - 2)z+ 1=0 We see that a= 1, b= - 2, and c= 1. Let's substitute these values into the formula, and solve for z.
z=- b±sqrt(b^2-4ac)/2a
z=- ( - 2)±sqrt(( - 2)^2-4( 1)( 1))/2( 1)
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Solve for z
z=2±sqrt((- 2)^2-4(1)(1))/2(1)
z=2±sqrt(4-4(1)(1))/2(1)
z=2±sqrt(4-4)/2
z=2±sqrt(0)/2
z=2± 0/2
The solutions for this equation are z= 2± 02. Let's separate them by using the positive and negative signs.
z=2± 0/2
z=2+0/2 z=2-0/2
z=2/2 z=2/2
z=1 z=1
We found that the solution for z^2-2z+1=0 is z=1. This means that x^2=1. Let's solve this equation!
x^2=1
x=± 1
We found that the zeros of f(x)=3x^4-6x^2+3 are x=- 1 and x=1.

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 3x^4-6x^2+3 f(x)=3x^4-6x^2+3
- 2 3( - 2)^4-6( - 2)^2+3 27
0 3( 0)^4-6( 0)^2+3 3
2 3( 2)^4-6( 2)^2+3 27

The points ( - 2, 27), ( 0, 3), and ( 2, 27) are on the graph of the function. We can also see that the leading coefficient is 3, which is a positive number. Also, the degree is 4, which is an even number. Therefore, the end behavior is up and up. Now, let's draw the graph!