Sketch the graph of the polynomial function $$ p(x) = x^3-21x^2+145x-323 $$

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

To find the x-intercepts solve, the equation $ \color{blue}{ x^3-21x^2+145x-323 = 0 } $

The solution of this equation is:

$$ \begin{matrix}x = 4.82 \end{matrix} $$

(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^3-21x^2+145x-323 } $, so:

$$ \text{Y inercept} = p(0) = -323 $$

STEP 3:Find the end behavior

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

$$ \lim_{x \to -\infty} \left( x^3-21x^2+145x-323 \right) = \lim_{x \to -\infty} x^3 = \color{blue}{ -\infty } $$

The graph starts in the lower-left corner.

$$ \lim_{x \to \infty} \left( x^3-21x^2+145x-323 \right) = \lim_{x \to \infty} x^3 = \color{blue}{ \infty } $$

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) $:

$$ p^{\prime} (x) = 3x^2-42x+145 $$

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

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x_1 = 7.8165 & x_2 = 6.1835 \end{matrix} $$

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

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 7.8165 } \Rightarrow p\left(7.8165\right) = \color{orangered}{ 4.9113 }\\[1 em] \text{for } ~ x & = \color{blue}{ 6.1835 } \Rightarrow p\left(6.1835\right) = \color{orangered}{ 7.0887 }\end{aligned} $$

So the turning points are:

$$ \begin{matrix} \left( 7.8165, 4.9113 \right) & \left( 6.1835, 7.0887 \right)\end{matrix} $$

STEP 5:Find the inflection points

The inflection points are located at zeroes of second derivative. The second derivative is $ p^{\prime \prime} (x) = 6x-42 $.

The zero of second derivative is

$$ \begin{matrix}x = 7 \end{matrix} $$

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 7 } \Rightarrow p\left(7\right) = \color{orangered}{ 6 }\end{aligned} $$

So the inflection point is:

$$ \begin{matrix} \left( 7, 6 \right)\end{matrix} $$

Graphing Polynomials