Sketch the graph of the polynomial function $$ p(x) = x^6-9x^4+24x^2-16 $$

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

To find the x-intercepts solve, the equation $ \color{blue}{ x^6-9x^4+24x^2-16 = 0 } $

The solutions of this equation are:

$$ \begin{matrix}x_1 = 1 & x_2 = 2 & x_3 = -1 & x_4 = -2 & x_5 = 2 & x_6 = -2 \end{matrix} $$

(you can use the step-by-step polynomial equation solver to see a detailed explanation of how to solve the equation)

STEP 2:Find the y-intercepts

To find the y-intercepts, substitute $ x = 0 $ into $ \color{blue}{ p(x) = x^6-9x^4+24x^2-16 } $, so:

$$ \text{Y inercept} = p(0) = -16 $$

STEP 3:Find the end behavior

The end behavior of a polynomial is the same as the end behavior of a leading term.

$$ \lim_{x \to -\infty} \left( x^6-9x^4+24x^2-16 \right) = \lim_{x \to -\infty} x^6 = \color{blue}{ \infty } $$

The graph starts in the upper-left corner.

$$ \lim_{x \to \infty} \left( x^6-9x^4+24x^2-16 \right) = \lim_{x \to \infty} x^6 = \color{blue}{ \infty } $$

The graph ends in the upper-right corner.

STEP 4:Find the turning points

To determine the turning points, we need to find the first derivative of $ p(x) $:

$$ p^{\prime} (x) = 6x^5-36x^3+48x $$

The x coordinate of the turning points are located at the zeros of the first derivative

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x_1 = 0 & x_2 = 2 & x_3 = -2 & x_4 = \sqrt{ 2 } & x_5 = -\sqrt{ 2 } \end{matrix} $$

(cleck here to see a explanation of how to solve the equation)

To find the y coordinates, substitute the above values into $ p(x) $

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0 } \Rightarrow p\left(0\right) = \color{orangered}{ -16 }\\[1 em] \text{for } ~ x & = \color{blue}{ 2 } \Rightarrow p\left(2\right) = \color{orangered}{ 0 }\\[1 em] \text{for } ~ x & = \color{blue}{ -2 } \Rightarrow p\left(-2\right) = \color{orangered}{ 0 }\\[1 em] \text{for } ~ x & = \color{blue}{ \sqrt{ 2 } } \Rightarrow p\left(\sqrt{ 2 }\right) = \color{orangered}{ 4 }\\[1 em] \text{for } ~ x & = \color{blue}{ -\sqrt{ 2 } } \Rightarrow p\left(-\sqrt{ 2 }\right) = \color{orangered}{ 4 }\end{aligned} $$

So the turning points are:

$$ \begin{matrix} \left( 0, -16 \right) & \left( 2, 0 \right) & \left( -2, 0 \right) & \left( \sqrt{ 2 }, 4 \right) & \left( -\sqrt{ 2 }, 4 \right)\end{matrix} $$

STEP 5:Find the inflection points

The inflection points are located at zeroes of second derivative. The second derivative is $ p^{\prime \prime} (x) = 30x^4-108x^2+48 $.

The zeros of second derivative are

$$ \begin{matrix}x_1 = -0.7207 & x_2 = 0.7207 & x_3 = 1.7552 & x_4 = -1.7552 \end{matrix} $$

Substitute the x values into $ p(x) $ to get y coordinates

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ -0.7207 } \Rightarrow p\left(-0.7207\right) = \color{orangered}{ -5.8226 }\\[1 em] \text{for } ~ x & = \color{blue}{ 0.7207 } \Rightarrow p\left(0.7207\right) = \color{orangered}{ -5.8226 }\\[1 em] \text{for } ~ x & = \color{blue}{ 1.7552 } \Rightarrow p\left(1.7552\right) = \color{orangered}{ 1.7587 }\\[1 em] \text{for } ~ x & = \color{blue}{ -1.7552 } \Rightarrow p\left(-1.7552\right) = \color{orangered}{ 1.7587 }\end{aligned} $$

So the inflection points are:

$$ \begin{matrix} \left( -0.7207, -5.8226 \right) & \left( 0.7207, -5.8226 \right) & \left( 1.7552, 1.7587 \right) & \left( -1.7552, 1.7587 \right)\end{matrix} $$

Graphing Polynomials