Sketch the graph of the polynomial function $$ p(x) = 3x^7+2x^6+x^5+5x^4+6x^3-7x^2-8x-9 $$

Tap the blue points to see coordinates.

STEP 1:Find the x-intercepts

To find the x-intercepts solve, the equation $ \color{blue}{ 3x^7+2x^6+x^5+5x^4+6x^3-7x^2-8x-9 = 0 } $

The solution of this equation is:

$$ \begin{matrix}x = 1.0996 \end{matrix} $$

(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^7+2x^6+x^5+5x^4+6x^3-7x^2-8x-9 } $, so:

$$ \text{Y inercept} = p(0) = -9 $$

STEP 3:Find the end behavior

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

$$ \lim_{x \to -\infty} \left( 3x^7+2x^6+x^5+5x^4+6x^3-7x^2-8x-9 \right) = \lim_{x \to -\infty} 3x^7 = \color{blue}{ -\infty } $$

The graph starts in the lower-left corner.

$$ \lim_{x \to \infty} \left( 3x^7+2x^6+x^5+5x^4+6x^3-7x^2-8x-9 \right) = \lim_{x \to \infty} 3x^7 = \color{blue}{ \infty } $$

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) $:

$$ p^{\prime} (x) = 21x^6+12x^5+5x^4+20x^3+18x^2-14x-8 $$

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

$$ p^{\prime} (x) = 0 $$ $$ \begin{matrix}x_1 = 0.652 & x_2 = -0.4358 \end{matrix} $$

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

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0.652 } \Rightarrow p\left(0.652\right) = \color{orangered}{ -14.2034 }\\[1 em] \text{for } ~ x & = \color{blue}{ -0.4358 } \Rightarrow p\left(-0.4358\right) = \color{orangered}{ -7.1703 }\end{aligned} $$

So the turning points are:

$$ \begin{matrix} \left( 0.652, -14.2034 \right) & \left( -0.4358, -7.1703 \right)\end{matrix} $$

STEP 5:Find the inflection points

The inflection points are located at zeroes of second derivative. The second derivative is $ p^{\prime \prime} (x) = 126x^5+60x^4+20x^3+60x^2+36x-14 $.

The zero of second derivative is

$$ \begin{matrix}x = 0.2576 \end{matrix} $$

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

$$ \begin{aligned} \text{for } ~ x & = \color{blue}{ 0.2576 } \Rightarrow p\left(0.2576\right) = \color{orangered}{ -11.3983 }\end{aligned} $$

So the inflection point is:

$$ \begin{matrix} \left( 0.2576, -11.3983 \right)\end{matrix} $$

Graphing Polynomials