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

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

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

The solutions of this equation are:

$$ \begin{matrix}x_1 = -1 & x_2 = 1.8201 \end{matrix} $$

(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^4-4x^3-2x^2+x-4 } $, so:

$$ \text{Y inercept} = p(0) = -4 $$

STEP 3:Find the end behavior

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

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

The graph starts in the upper-left corner.

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

The graph ends in the upper-right corner.

STEP 4:Find the turning points

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

$$ p^{\prime} (x) = 12x^3-12x^2-4x+1 $$

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

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x_1 = 0.1746 & x_2 = -0.3921 & x_3 = 1.2176 \end{matrix} $$

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

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0.1746 } \Rightarrow p\left(0.1746\right) = \color{orangered}{ -3.9049 }\\[1 em] \text{for } ~ x & = \color{blue}{ -0.3921 } \Rightarrow p\left(-0.3921\right) = \color{orangered}{ -4.3875 }\\[1 em] \text{for } ~ x & = \color{blue}{ 1.2176 } \Rightarrow p\left(1.2176\right) = \color{orangered}{ -6.3742 }\end{aligned} $$

So the turning points are:

$$ \begin{matrix} \left( 0.1746, -3.9049 \right) & \left( -0.3921, -4.3875 \right) & \left( 1.2176, -6.3742 \right)\end{matrix} $$

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^2-24x-4 $.

The zeros of second derivative are

$$ \begin{matrix}x_1 = 0.8047 & x_2 = -0.1381 \end{matrix} $$

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0.8047 } \Rightarrow p\left(0.8047\right) = \color{orangered}{ -5.3169 }\\[1 em] \text{for } ~ x & = \color{blue}{ -0.1381 } \Rightarrow p\left(-0.1381\right) = \color{orangered}{ -4.1646 }\end{aligned} $$

So the inflection points are:

$$ \begin{matrix} \left( 0.8047, -5.3169 \right) & \left( -0.1381, -4.1646 \right)\end{matrix} $$

Graphing Polynomials