Big Ideas Math Algebra 1, 2015
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Big Ideas Math Algebra 1, 2015 View details
5. Using Intercept Form
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Exercise 68 Page 456

Rewrite the function in the intercept form and use the Zero Product Property to find its zeros.

Practice makes perfect

To draw the graph of the given function, we will follow four steps.

  1. Rewrite the polynomial function in intercept form.
  2. Identify the zeros of the function.
  3. Find some additional points and consider end behaviour.
  4. Plot the previously found points and draw the graph through them.

Let's go through these steps one at a time.

Rewrite the Function

We will start by rewriting the function in intercept form. To do so, we will factor the right-hand side of the given equation.
g(x)=6x^3+30x^2-36x
g(x)=6x(x^2+5x-6)
g(x)=6x(x^2-x+6x-6)
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Factor out x & 6
g(x)=6x(x(x-1)+6x-6)
g(x)=6x(x(x-1)+6(x-1))
g(x)=6x(x-1)(x+6)

Zeros of the Function

Now we want to find the zeros of the polynomial function. g(x)=6x(x-1)(x+6) To do so, we need to find the values of x for which g(x)=0. g(x)=0 ⇔ 6x(x-1)(x+6)=0 We will use the Zero Product Property to solve the equation.
6x(x-1)(x+6)=0
lc6x=0 & (I) x-1=0 & (II) x+6=0 & (III)
lx=0 x-1=0 x+6=0
lx=0 x=1 x+6=0
lx=0 x=1 x=- 6
We found that the zeros of the function are 0, 1 and - 6.

Additional Points and End Bahaviour

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

x 6x^3+30x^2-36x g(x)=6x^3+30x^2-36x
- 5 6( - 5)^3+30( - 5)^2-36( - 5) 180
- 3 6( - 3)^3+30( - 3)^2-36( - 3) 216
- 1 6( - 1)^3+30( - 1)^2-36( - 1) 60
0.5 6( 0.5)^3+30( 0.5)^2-36( 0.5) - 9.75
2 6( 2)^3+30( 2)^2-36( 2) 96

The points ( - 5, 180), ( - 3, 216), ( - 1, 60), ( 0.5, - 9.75) and ( 2, 96) are on the graph of the function. Finally, as we already have the standard form of our function we can determine the leading coefficient and degree of the polynomial function. g(x)= 6x^3+30x^2-36x We can see that the leading coefficient is 6, which is a positive number. Also, the degree is 3, which is an odd number. Therefore, the end behavior is down and up.

Graph

Now, let's draw the graph through our points, considering the end behaviour.