Sketch the graph of the polynomial function $$ p(x) = \frac{1}{5}x^5-2x^3+\frac{9}{5}x $$

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

To find the x-intercepts solve, the equation $ \color{blue}{ \frac{1}{5}x^5-2x^3+\frac{9}{5}x = 0 } $

The solutions of this equation are:

$$ \begin{matrix}x_1 = 0 & x_2 = 1 & x_3 = 3 & x_4 = -1 & x_5 = -3 \end{matrix} $$

(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) = \frac{1}{5}x^5-2x^3+\frac{9}{5}x } $, 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.

$$ \lim_{x \to -\infty} \left( \frac{1}{5}x^5-2x^3+\frac{9}{5}x \right) = \lim_{x \to -\infty} \frac{1}{5}x^5 = \color{blue}{ -\infty } $$

The graph starts in the lower-left corner.

$$ \lim_{x \to \infty} \left( \frac{1}{5}x^5-2x^3+\frac{9}{5}x \right) = \lim_{x \to \infty} \frac{1}{5}x^5 = \color{blue}{ \infty } $$

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) $:

$$ p^{\prime} (x) = x^4-6x^2+\frac{9}{5} $$

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

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x_1 = 0.5628 & x_2 = -0.5628 & x_3 = -2.384 & x_4 = 2.384 \end{matrix} $$

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

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0.5628 } \Rightarrow p\left(0.5628\right) = \color{orangered}{ 0.6678 }\\[1 em] \text{for } ~ x & = \color{blue}{ -0.5628 } \Rightarrow p\left(-0.5628\right) = \color{orangered}{ -0.6678 }\\[1 em] \text{for } ~ x & = \color{blue}{ -2.384 } \Rightarrow p\left(-2.384\right) = \color{orangered}{ 7.4061 }\\[1 em] \text{for } ~ x & = \color{blue}{ 2.384 } \Rightarrow p\left(2.384\right) = \color{orangered}{ -7.4061 }\end{aligned} $$

So the turning points are:

$$ \begin{matrix} \left( 0.5628, 0.6678 \right) & \left( -0.5628, -0.6678 \right) & \left( -2.384, 7.4061 \right) & \left( 2.384, -7.4061 \right)\end{matrix} $$

STEP 5:Find the inflection points

The inflection points are located at zeroes of second derivative. The second derivative is $ p^{\prime \prime} (x) = 4x^3-12x $.

The zeros of second derivative are

$$ \begin{matrix}x_1 = 0 & x_2 = \sqrt{ 3 } & x_3 = -\sqrt{ 3 } \end{matrix} $$

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0 } \Rightarrow p\left(0\right) = \color{orangered}{ 0 }\\[1 em] \text{for } ~ x & = \color{blue}{ \sqrt{ 3 } } \Rightarrow p\left(\sqrt{ 3 }\right) = \color{orangered}{ -12 \frac{\sqrt{ 3 }}{ 5 } }\\[1 em] \text{for } ~ x & = \color{blue}{ -\sqrt{ 3 } } \Rightarrow p\left(-\sqrt{ 3 }\right) = \color{orangered}{ \frac{ 12 \sqrt{ 3}}{ 5 } }\end{aligned} $$

So the inflection points are:

$$ \begin{matrix} \left( 0, 0 \right) & \left( \sqrt{ 3 }, -12 \dfrac{\sqrt{ 3 }}{ 5 } \right) & \left( -\sqrt{ 3 }, \dfrac{ 12 \sqrt{ 3}}{ 5 } \right)\end{matrix} $$

Graphing Polynomials