Sketch the graph of the polynomial function $$ p(x) = 3x^4-33x-6x^2+8x $$

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

To find the x-intercepts solve, the equation $ \color{blue}{ 3x^4-33x-6x^2+8x = 0 } $

The solutions of this equation are:

$$ \begin{matrix}x_1 = 0 & x_2 = 2.3538 \end{matrix} $$

(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) = 3x^4-33x-6x^2+8x } $, so:

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

STEP 3:Find the end behavior

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

$$ \lim_{x \to -\infty} \left( 3x^4-33x-6x^2+8x \right) = \lim_{x \to -\infty} 3x^4 = \color{blue}{ \infty } $$

The graph starts in the upper-left corner.

$$ \lim_{x \to \infty} \left( 3x^4-33x-6x^2+8x \right) = \lim_{x \to \infty} 3x^4 = \color{blue}{ \infty } $$

The graph ends in the upper-right corner.

STEP 4:Find the turning points

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

$$ p^{\prime} (x) = 12x^3-12x-25 $$

The x coordinate of the turning point is located at the zeros of the first derivative

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x = 1.5353 \end{matrix} $$

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

To find the y coordinate, substitute the above value into $ p(x) $

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 1.5353 } \Rightarrow p\left(1.5353\right) = \color{orangered}{ -35.857 }\end{aligned} $$

So the turning point is:

$$ \begin{matrix} \left( 1.5353, -35.857 \right)\end{matrix} $$

STEP 5:Find the inflection points

The inflection points are located at zeroes of second derivative. The second derivative is $ p^{\prime \prime} (x) = 36x^2-12 $.

The zeros of second derivative are

$$ \begin{matrix}x_1 = \dfrac{\sqrt{ 3 }}{ 3 } & x_2 = - \dfrac{\sqrt{ 3 }}{ 3 } \end{matrix} $$

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ \frac{\sqrt{ 3 }}{ 3 } } \Rightarrow p\left(\frac{\sqrt{ 3 }}{ 3 }\right) = \color{orangered}{ -16.1004 }\\[1 em] \text{for } ~ x & = \color{blue}{ - \frac{\sqrt{ 3 }}{ 3 } } \Rightarrow p\left(- \frac{\sqrt{ 3 }}{ 3 }\right) = \color{orangered}{ 12.7671 }\end{aligned} $$

So the inflection points are:

$$ \begin{matrix} \left( \dfrac{\sqrt{ 3 }}{ 3 }, -16.1004 \right) & \left( - \dfrac{\sqrt{ 3 }}{ 3 }, 12.7671 \right)\end{matrix} $$

Graphing Polynomials